There are two messengers as Messiah explains in Matthew 11.
Notice that in the verse that messenger is said to be "even the Lord"(NOT the LORD, this is crucial), and whom Israel "seeks," and "delights in," which are VERY strong terms coming from their own God, to whom alone they should do these two things, being a "Jealous God."
The reason is, that messenger is the angel of presence, these whom alone can refer to themselves as though they were the Almighty Himself.
And the angel of the LORD said unto him, Wherefore hast thou smitten thine ass these three times? behold, I went out to withstand thee, because thy way is perverse before me .
2 And the angel of the LORD appeared to him in a blazing fire from the midst of a bush; and he looked, and behold, the bush was burning with fire, yet the bush was not consumed.
4 When the LORD saw that he turned aside to look, God called to him from the midst of the bush, and said, “Moses, Moses!” And he said, “Here I am.”
5 Then He said, “Do not come near here; remove your sandals from your feet, for the place on which you are standing is holy ground.”
6 He said also, “I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob.” Then Moses hid his face, for he was afraid to look at God.
Note how it reads, "the angel appeared as a burning bush" yet it says" Moses feared to look upon God''...
7 And the LORD said, “I have surely seen the affliction of My people who are in Egypt, and have given heed to their cry because of their taskmasters, for I am aware of their sufferings.
8“So I have come down to deliver them from the power of the Egyptians...
The angel doesn't say "the LORD has sent me.."
Not forgetting about the ‘friend of God’’ in Genesis.
Notice the distinction in identity of the characters that met Abraham, in the verse below;
And the men rose up from thence, and looked toward Sodom: and Abraham went with them to bring them on the way...
20 And the LORD said, Because the cry of Sodom and Gomorrah is great, and because their sin is very grievous;
21 I will go down now, and see whether they have done altogether according to the cry of it, which is come unto me; and if not, I will know.
22 And the men turned their faces from thence, and went toward Sodom: but Abraham stood yet before the LORD.
23 And Abraham drew near, and said, Wilt thou also destroy the righteous with the wicked?
So these 'men' who headed for Sodom leaving Abraham are later on at Lot’s place revealed to be angels, and who hint at their deference to another in Gen 19:22.
They left Abraham in the presence of one whom Abraham addresses as the ‘judge of all the earth,’ in verse 25, and to which the being before him replied in acknowledgement to His statements;
25 That be far from thee to do after this manner, ...Shall not the Judge of all the earth do right?
26 And the LORD said, If I find in Sodom fifty righteous within the city..
This is the kind of messenger of the covenant here, "the Lord whom you seek"..."the messenger whom you delight in", which seeking and delight are terms singularly used in circumstances of worship and concerning Israel, and worship which should be for the Most High ALONE.
Cases of this ‘delighting’ being one of God's dues are in;
Delight thyself also in the Lord ; and he shall give thee the desires of thine heart.
And in Isaiah 58 where both terms are used.
Yet they seek me daily, and delight to know my ways, as a nation that did righteousness, and forsook not the ordinance of their God: they ask of me the ordinances of justice; they take delight in approaching to God.
Now what was the need for His coming to the temple when His name was already in the temple, as Solomon and the Most High both affirm in 2 Chron 7:15-16, besides which state of affairs, as far as Israel’s problems of the day were concerned due to their offending neighbours, they couldn't ask for a better?
One reason is because of the kind of temple the Most High had in mind, and which no man could build but by a messenger of the covenant.
This is the question to them in Isaiah 66:1 concerning His ideal house.
Specific covenants such as is meant here are indicated in scriptures as being spirit devices for making a people behave in a certain desired way to the pleasure of a higher spirit among them, that is, in circumstances of a relationship between such a people and that higher spirit.
This is the same covenant in Daniel 7 that a wicked spirit prince is said to "strengthen" with many for a week, and due to which these many are made desolate for a week, that is, rendered unproductive in matters of righteousness (Psalm 25:16), and that within a period signified as a week, which is qualified in verse as ‘until consummation,’ namely, until the norm shall have changed among men.
Now unlike the case of Daniel, the messenger of covenant here is for a power to the nation of Israel for righteousness’ sake.
This is the same ‘“Lord” in Isaiah 4:4 as opposed to the LORD as pointed out at the beginning, and who washes Israel by a spirit of judgment and a spirit of burning, the covenant of blood, because these are powers.
This is the covenant in;
As for thee also, by the blood of thy covenant I have sent forth thy prisoners out of the pit wherein [is] no water.
Again indicated a spirit device that wroughts a spiritual deliverance.
He is addressing the King of Israel that comes riding on the donkey, the one having salvation in Zech 9:9.
There’s only one such King written about associated with a temple, salvation and a covenant for the people, Messiah.
He is the messenger of the covenant.
I hope that helps.