Oil throughout the Bible represents service: How can oil represent salvation in: Mat_25:8 And the foolish said unto the wise, Give us of your oil; for our lamps are gone out.
I believe that the oil of salvation in this parable is representing the “oil of gladness” or joy.
We are commanded to “rejoice evermore”….that is, at all times. The "oil" of rejoicing should be retained in our "vessels" at all times.
1 Thessalonians 5:16 KJV (16) Rejoice evermore.
The foolish did not rejoice evermore as their joy went out as they waited while the wise took the oil of gladness within them. They rejoiced always even though they all “slumbered and slept”.
Matthew 25:3-4 KJV (3) They that were foolish took their lamps, and took no oil with them: (4) But the wise took oil in their vessels with their lamps.
The “oil of gladness” is for the lamp that gives praise and thanks to God. The wise went out to meet Him with the open joy and praise while the foolish did not.
Light is sown for the righteous and gladness for the upright in heart. Their lamp burns brightly with their open rejoicing and praising of the Lord. The joy does not stay hidden within the heart but is shown forth with the mouth that sings His praise.
Psalms 97:11-12 KJV (11) Light is sown for the righteous, and gladness for the upright in heart. (12) Rejoice in the LORD, ye righteous; and give thanks at the remembrance of his holiness.
The wise were then able to “enter into the joy of the Lord”….the fullness of joy…as they entered in with Him to the marriage.
The wise heard His voice…the call…and rejoiced and were thankful. They were able to enter into the fullness of joy and knowing the mysteries of the kingdom while the foolish did not rejoice at what they heard and did not praise Him in thanksgiving. The foolish were not found "ready" as they did not rejoice.
Matthew 25:10-13 KJV (10) And while they went to buy, the bridegroom came; and they that were ready went in with him to the marriage: and the door was shut. (11) Afterward came also the other virgins, saying, Lord, Lord, open to us. (12) But he answered and said, Verily I say unto you, I know you not. (13) Watch therefore, for ye know neither the day nor the hour wherein the Son of man cometh.
We see in the marriage supper of the Lamb in Revelation 19 that a voice of a great multitude spoke and said….
Revelation 19:6-9 KJV (6) And I heard as it were the voice of a great multitude, and as the voice of many waters, and as the voice of mighty thunderings, saying, Alleluia: for the Lord God omnipotent reigneth.
…”let us be glad and rejoice and give honor to Him”….
(7) Let us be glad and rejoice, and give honour to him: for the marriage of the Lamb is come, and his wife hath made herself ready. (8) And to her was granted that she should be arrayed in fine linen, clean and white: for the fine linen is the righteousness of saints.
“Blessed”….that is, happier….are they which are called unto the marriage supper of the Lamb. The wise will be able to enter in to the fullness of joy…the joy of the Lord. Those who are called are to rejoice at what they hear the Spirit saying: the true sayings of God. The true sayings of God are like a “supper” to those who “eat” of it and are satisfied with what they hear as they rejoice even more and are thankful for His words.
(9) And he saith unto me, Write, Blessed are they which are called unto the marriage supper of the Lamb. And he saith unto me, These are the true sayings of God.
The Lord comes to serve us the “meat” of the Word of God….the true sayings of God…but we must be found ready with the oil of gladness within our vessels.
"Blessed"....that is, HAPPY...are those whom the Lord when He comes shall find watching. Those who are "watching" are found happy....rejoicing always with the oil of gladness within them.
Luke 12:35-37 KJV (35) Let your loins be girded about, and your lights burning; (36) And ye yourselves like unto men that wait for their lord, when he will return from the wedding; that when he cometh and knocketh, they may open unto him immediately. (37) Blessed are those servants, whom the lord when he cometh shall find watching: verily I say unto you, that he shall gird himself, and make them to sit down to meat, and will come forth and serve them.
It is about rejoicing in the LORD. “My soul shall be joyful in my God…”
Isaiah 61:10 KJV (10) I will greatly rejoice in the LORD, my soul shall be joyful in my God; for he hath clothed me with the garments of salvation, he hath covered me with the robe of righteousness, as a bridegroom decketh himself with ornaments, and as a bride adorneth herself with her jewels.
As John the Baptist said…the friend of the Bridegroom stands and hears Him (as He speaks the true words of God….the “supper”) and rejoices greatly because of His voice. His joy is then fulfilled.
John 3:28-29 KJV (28) Ye yourselves bear me witness, that I said, I am not the Christ, but that I am sent before him. (29) He that hath the bride is the bridegroom: but the friend of the bridegroom, which standeth and heareth him, rejoiceth greatly because of the bridegroom's voice: this my joy therefore is fulfilled.
His servants (whom He finds ready at the hearing of His voice calling them) will “eat” of the true sayings of God. They will rejoice and take in what they hear His voice saying and will be satisfied and will enter into the joy of the Lord in fullness while those who do not agree with what they hear in their anger shall go “hungry”.
Isaiah 65:13-14 KJV (13) Therefore thus saith the Lord GOD, Behold, my servants shall eat, but ye shall be hungry: behold, my servants shall drink, but ye shall be thirsty: behold, my servants shall rejoice, but ye shall be ashamed:
His servants will sing for joy of heart while those who resist what they hear and do not joy in it will cry for sorrow of heart…..
*(14) Behold, my servants shall sing for joy of heart, but ye shall cry for sorrow of heart, and shall howl for vexation of spirit
The answer to your question is that the Bible does not suggest that “oil only represents service”. Perhaps a better question would be to ask what the oil in the parable represents.
A full explanation of Jesus’ parable of the ten virgins and the significance of the oil in the lamps is given in this article: https://www.gotquestions.org/parable-ten-virgins.html
The olive oil used in the lamps can be interpreted as a symbol of the Holy Spirit, or the faith of the born-again believer. It does not represent “service” although the parable has to do with being on the alert for the return of Christ (the bridegroom). The article in the link below explains the uses of olive oil and what it symbolises.
Jesus gave the point of the parable: “Therefore keep watch, because you do not know the day or the hour” (Matthew 25:13). At the end of the age, when Jesus comes back, some will be ready for His arrival (illustrated by the wise virgins who had olive oil); others will not be ready (symbolized by the foolish virgins who had no oil). Considering the olive oil as a symbol of the Holy Spirit (or of faith), we could say that only those who have the Spirit (or faith in Christ) are truly ready for Jesus’ second coming. Source: https://www.gotquestions.org/olive-oil-symbol.html
Matthew 25 is basically one parable. Each individual parable conveys the notion of coming to the Lord expecting salvation, but having neglected basic tenets of His faith, such as charity:
Matthew 25 (DRB) 1 Then shall the kingdom of heaven be like to ten virgins, who taking their lamps went out to meet the bridegroom and the bride. 2 And five of them were foolish, and five wise. 3 But the five foolish, having taken their lamps, did not take oil with them: 4 But the wise took oil in their vessels with the lamps. 5 And the bridegroom tarrying, they all slumbered and slept. 6 And at midnight there was a cry made: Behold the bridegroom cometh, go ye forth to meet him. 7 Then all those virgins arose and trimmed their lamps. 8 And the foolish said to the wise: Give us of your oil, for our lamps are gone out. 9 The wise answered, saying: Lest perhaps there be not enough for us and for you, go ye rather to them that sell, and buy for yourselves. 10 Now whilst they went to buy, the bridegroom came: and they that were ready, went in with him to the marriage, and the door was shut. 11 But at last come also the other virgins, saying: Lord, Lord, open to us. 12 But he answering said: Amen I say to you, I know you not. 13 Watch ye therefore, because you know not the day nor the hour.
Preparedness. 2 Peter 3:14.
14 For even as a man going into a far country, called his servants, and delivered to them his goods; 15 And to one he gave five talents, and to another two, and to another one, to every one according to his proper ability: and immediately he took his journey. 16 And he that had received the five talents, went his way, and traded with the same, and gained other five. 17 And in like manner he that had received the two, gained other two. 18 But he that had received the one, going his way digged into the earth, and hid his lord's money. 19 But after a long time the lord of those servants came, and reckoned with them. 20 And he that had received the five talents coming, brought other five talents, saying: Lord, thou didst deliver to me five talents, behold I have gained other five over and above. 21 His lord said to him: Well done, good and faithful servant, because thou hast been faithful over a few things, I will place thee over many things: enter thou into the joy of thy lord. 22 And he also that had received the two talents came and said: Lord, thou deliveredst two talents to me: behold I have gained other two. 23 His lord said to him: Well done, good and faithful servant: because thou hast been faithful over a few things, I will place thee over many things: enter thou into the joy of thy lord. 24 But he that had received the one talent, came and said: Lord, I know that thou art a hard man; thou reapest where thou hast not sown, and gatherest where thou hast not strewed. 25 And being afraid I went and hid thy talent in the earth: behold here thou hast that which is thine. 26 And his lord answering, said to him: Wicked and slothful servant, thou knewest that I reap where I sow not, and gather where I have not strewed: 27 Thou oughtest therefore to have committed my money to the bankers, and at my coming I should have received my own with usury. 28 Take ye away therefore the talent from him, and give it to him that hath ten talents. 29 For to every one that hath shall be given, and he shall abound: but from him that hath not, that also which he seemeth to have shall be taken away. 30 And the unprofitable servant cast ye out into the exterior darkness. There shall be weeping and gnashing of teeth.
31 And when the Son of man shall come in his majesty, and all the angels with him, then shall he sit upon the seat of his majesty. 32 And all nations shall be gathered together before him, and he shall separate them one from another, as the shepherd separateth the sheep from the goats: 33 And he shall set the sheep on his right hand, but the goats on his left. 34 Then shall the king say to them that shall be on his right hand: Come, ye blessed of my Father, possess you the kingdom prepared for you from the foundation of the world. 35 For I was hungry, and you gave me to eat; I was thirsty, and you gave me to drink; I was a stranger, and you took me in: 36 Naked, and you covered me: sick, and you visited me: I was in prison, and you came to me. 37 Then shall the just answer him, saying: Lord, when did we see thee hungry, and fed thee; thirsty, and gave thee drink? 38 And when did we see thee a stranger, and took thee in? or naked, and covered thee? 39 Or when did we see thee sick or in prison, and came to thee? 40 And the king answering, shall say to them: Amen I say to you, as long as you did it to one of these my least brethren, you did it to me. 41 Then he shall say to them also that shall be on his left hand: Depart from me, you cursed, into everlasting fire which was prepared for the devil and his angels. 42 For I was hungry, and you gave me not to eat: I was thirsty, and you gave me not to drink. 43 I was a stranger, and you took me not in: naked, and you covered me not: sick and in prison, and you did not visit me. 44 Then they also shall answer him, saying: Lord, when did we see thee hungry, or thirsty, or a stranger, or naked, or sick, or in prison, and did not minister to thee? 45 Then he shall answer them, saying: Amen I say to you, as long as you did it not to one of these least, neither did you do it to me. 46 And these shall go into everlasting punishment: but the just, into life everlasting.
Point being: just and unjust correspond to your being.. just or unjust, not some association only in name with "Lord, Lord."