The quote is made when after Jesus using his power to heal the sick, cast out demons and in short, forgive sins. Scribes came down to him accusing him working hand and hand with Satan to accomplish these tasks.
And the scribes which came down from Jerusalem said, He hath Beelzebub, and by the prince of the devils casteth he out devils
Additionally, this is a result of the Son of God ordaining his 12 apostles to do those same works.
And he ordained twelve, that they should be with him, and that he might send them forth to preach, And to have power to heal sicknesses, and to cast out devils
What we see here is Christ giving his authority to his Bishops, These bishops are with us now and continue to excercise this Christ given authority.
Further on you will see that Christ changes his mind and just tells everyone they can just whisper a little prayer up in the air and excercise these powers.
oh wait, there is not biblical basis for that.
There are commisions given to the Disciples here, These commissions are Graces imparted what we now call Sacrements, not to them only but to thier office which continues as part of the church. That commission is here:
Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you. And when he had so said, he shewed unto them his hands and his side. Then were the disciples glad, when they saw the Lord. Then said Jesus to them again, Peace be unto you:as my Father hath sent me, even so send I you. And when he had said this, he breathed on them, and saith unto them, Receive ye the Holy Ghost: Whose soever sins ye remit, they are remitted unto them; and whose soever sins ye retain, they are retained
This commision was given to his disciples by breathing on them. This breath which came from the mouth of God was real and not a symbol, it had power, in this case, power given to them directly by God to forgive sins and cast out demons and heal the sick. This power is being pased on now by those who faithfully maintain the faith.
The office is here
For it is written in the book of Psalms, Let his habitation be desolate, and let no man dwell therein:and his bishoprick let another take.
It is indeed written here:
Let their habitation be desolate;
and let none dwell in their tents they persecute him whom thou hast smitten;
and they talk to the grief of those whom thou hast wounded.
Add iniquity unto their iniquity:
and let them not come into thy righteousness.
But also summing up the Psalm:
For God will save Zion,
and will build the cities of Judah:
that they may dwell there, and have it in possession.
The seed also of his servants shall inherit it:
and they that love his name shall dwell therein
Let his days be few;
and let another take his office
with the conclusion for those who take over his office.
Now I praise you, brethren, that ye remember me in all things, and keep the ordinances, as I delivered them to you
1 Cor 11:2
Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle
2 Th 2:15
and warnings of those who forget
From which some having swerved have turned aside unto vain jangling; Desiring to be teachers of the law; understanding neither what they say, nor whereof they affirm
1 Tim 1:6
Neglect not the gift that is in thee, which was given thee by prophecy, with the laying on of the hands of the presbytery. Meditate upon these things; give thyself wholly to them; that thy profiting may appear to all. Take heed unto thyself, and unto the doctrine; continue in them:for in doing this thou shalt both save thyself, and them that hear thee
1 Tim 4:14
I charge thee before God, and the Lord Jesus Christ, and the elect angels, that thou observe these things without preferring one before another, doing nothing by partiality. Lay hands suddenly on no man, neither be partaker of other men's sins:keep thyself pure
1 Tim 5:22
So what it meant by our Lord when he makes this statement is that all sins will be forgiven, and this is how, I will appoint others, as he just had done, Not as a tool of Satan against Satan, but as a tool of God against Satin and Sin. He created a ministry outlined above in the New Testiment versus and fullfilled in his Church, a Church being built over the last 2000 years. All the sins that will be forgiven are the ones that have been forgiven by the Church through it's ministers, by Chirst acting on his own, as he has not given up his athority but shared it, and by God the father, who through a means known only to God himself, can forgive sins, this last mystery known only to God.
The passage does not suggest, that if you do not repent or that you continue to sin against God, that you are forgiven automatically, only that those who he sent in the flesh with the power of the Holy Spirit acting in and Through Christ have this power.