Angels speak on behalf of G-d - Key Passages

Tanakh consistently uses a style where the angel that is sent to the human to convey a message, speaks on behalf of G-d in a way that it seems like the angel has the power to make the promise happen. It almost seems G-d has come down to the human and is speaking to the human.

These passages are telling that this is what G-d told me to tell you and it will happen.

Genesis 16:10 And the angel of the Lord said to her, "I will greatly multiply your seed, and it will not be counted for abundance." - This is the event where an angel makes a promise to multiply Hagar's seed on behalf of G-d.

Genesis 18:1 Now the Lord appeared to him in the plains of Mamre, and he was sitting at the entrance of the tent when the day was hot. 2 And he lifted his eyes and saw, and behold, three men were standing beside him, and he saw and he ran toward them from the entrance of the tent, and he prostrated himself to the ground. 10 And he said, "I will surely return to you at this time next year, and behold, your wife Sarah will have a son." And Sarah heard from the entrance of the tent, and it was behind him. - Three men [angels] come to Abraham. The main man [angel] came to make the promise of Isaac, the second man[angel] came to rescue Lot and the third man [angel] came to destroy Sodom & Gomorrah. Here the main angel tells Abraham that at this time next year, Sarah will give birth to Isaac. 

Genesis 18:17 And the Lord said, "Shall I conceal from Abraham what I am doing?18 And Abraham will become a great and powerful nation, and all the nations of the world will be blessed in him. 19 For I have known him because he commands his sons and his household after him, that they should keep the way of the Lord to perform righteousness and justice, in order that the Lord bring upon Abraham that which He spoke concerning him." 33 And the Lord departed when He finished speaking to Abraham, and Abraham returned to his place. - Though the passage says it was G-d who was speaking to Abraham while the other 2 men went to Sodom & Gomorrah it is the main man [angel] that is speaking to Abraham

Genesis 21:17 And God heard the lad's voice, and an angel of God called to Hagar from heaven, and said to her, "What is troubling you, Hagar? Fear not, for God has heard the lad's voice in the place where he is. 18 Rise, pick up the lad and grasp your hand upon him, for I shall make him into a great nation."

Genesis 22:11 And an angel of God called to him from heaven and said, "Abraham! Abraham!" And he said, "Here I am." 12 And he said, "Do not stretch forth your hand to the lad, nor do the slightest thing to him, for now I know that you are a God fearing man, and you did not withhold your son, your only one, from Me."

Exodus 3:2 An angel of the Lord appeared to him in a flame of fire from within the thorn bush, and behold, the thorn bush was burning with fire, but the thorn bush was not being consumed. 4 The Lord saw that he had turned to see, and God called to him from within the thorn bush, and He said, "Moses, Moses!" And he said, "Here I am!" 6 And He said, "I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob." And Moses hid his face because he was afraid to look toward God. 7 And the Lord said, "I have surely seen the affliction of My people who are in Egypt, and I have heard their cry because of their slave drivers, for I know their pains. 8 I have descended to rescue them from the hand[s] of the Egyptians and to bring them up from that land, to a good and spacious land, to a land flowing with milk and honey, to the place of the Canaanites, the Hittites, the Amorites, the Perizzites, the Hivvites, and the Jebusites.

Exodus 13:21 And the Lord went before them by day in a pillar of cloud to cause it to lead them on the way and at night in a pillar of fire to give them light, [they thus could] travel day and night. 22 He did not move away the pillar of cloud by day or the pillar of fire at night [from] before the people. 19 Then the angel of God, who had been going in front of the Israelite camp, moved and went behind them, and the pillar of cloud moved away from in front of them and stood behind them. 20 And he came between the camp of Egypt and the camp of Israel, and there were the cloud and the darkness, and it illuminated the night, and one did not draw near the other all night long.

Numbers 22:34 Balaam said to the angel of the Lord, "I have sinned, for I did not know that you were standing on the road before me. Now, if it displeases you, I will return." 35 The angel of the Lord said to Balaam, "Go with these men, but the word I will speak to you-that you shall speak." So Balaam went with Balak's dignitaries.

Judges 6:12 And the angel of the Lord appeared and said to him, "The Lord is with you, mighty man of valor." 13 And Gideon said to him, "Please my lord, if the Lord be with us, why then has all this befallen us? And where are all His wonders which our forefathers told us, saying, 'Did not the Lord bring us up from Egypt?' But now the Lord has forsaken us, and He has delivered us into the hand of Midian." 14 And the Lord turned toward him and said, "Go, with this your strength, and save Israel from the hand of Midian. Have I not sent you?" 16 And the Lord said to him, "Because I shall be with you, and you shall strike Midian as one man." 22 Now Gideon saw that he was an angel of the Lord, and Gideon said, "Alas, O Lord God! Because I have seen the angel of the Lord face to face." 23 And the Lord said to him, "Peace be to you, fear not, you shall not die."

1 Samuel 3:10 And the Lord came and stood, and He called as at the other times, "Samuel! Samuel!" And Samuel said, "Speak, for Your bondsman is listening."