Angels praise God

Psalm 103:20-21 Praise the LORD, you his angels, you mighty ones who do his bidding, who obey his word. Praise the LORD, all his heavenly hosts, you his servants who do his will.

(See also Psalm 148:2 Praise him, all his angels; praise him, all his heavenly hosts.)

Angels have good reason to praise God - For their creation by God, for their preservation, for their happiness, in which they continue as they are elect of God in Christ.

They are always employed in the work of praising the Lord nor are they in the least backward in it, nor remiss. That is not why they are addressed as they are. Rather the design of the psalmist is only to show how great and good the Lord is and that angels, as great as they are, are under an obligation to praise him, and are bound to do so. He also intends to stir himself and others to this work, from such a consideration - that such noble creatures praise God.

C H Spurgeon

Finding his work of praise growing upon his hands, he calls upon "the firstborn sons of light" to speak the praises of the Lord, as well they may, for as Milton says, they best can tell. Dwelling nearer to that prepared throne than we as yet have leave to climb, they see in nearer vision the glory which we would adore. To them is given an exceeding might of intellect, and voice, and force which they delight to use in sacred services for him; let them now turn all their strength into that solemn song which we would send up to the third heaven. To him who gave angelic strength let all angelic strength be given. They are his angels, and therefore they are not loath to ring out his praises.

Angels will be judged one day - by believers

Paul says

1 Cor 6:3 Do you not know that we will judge angels? How much more the things of this life!

There is some mystery here but at the very least we can say that some angels will be judged and that believers will have some part in that judgement. No doubt that part will be a confirmatory one rather than anything more reliant on our own decisions. The fallen angels will be condemned to hell and the good angels will be confirmed for heaven. No doubt the focus lies on the fallen angels.

Angels revealed and announced the resurrection of Christ

Matthew 28:2-7 There was a violent earthquake, for an angel of the Lord came down from heaven and, going to the tomb, rolled back the stone and sat on it. His appearance was like lightning, and his clothes were white as snow. The guards were so afraid of him that they shook and became like dead men. The angel said to the women, "Do not be afraid, for I know that you are looking for Jesus, who was crucified. He is not here; he has risen, just as he said. Come and see the place where he lay. Then go quickly and tell his disciples: 'He has risen from the dead and is going ahead of you into Galilee. There you will see him.' Now I have told you."

Luke 24:2-7 They found the stone rolled away from the tomb, but when they entered, they did not find the body of the Lord Jesus. While they were wondering about this, suddenly two men in clothes that gleamed like lightning stood beside them. In their fright the women bowed down with their faces to the ground, but the men said to them, "Why do you look for the living among the dead? He is not here; he has risen! Remember how he told you, while he was still with you in Galilee: 'The Son of Man must be delivered over to the hands of sinners, be crucified and on the third day be raised again.'"