I will declare thy name - I will make thee known; that is, thine existence; thy perfections; thy law; thy method of salvation. As the result or effect of the interposition which he desired, and for which he prayed, he says that he would diffuse a knowledge of God. This is an expression of true piety, and is a statement of what in a pure mind will always be consequent on a gracious divine interposition - a purpose to make the character of the benefactor known. Compare Psalms 51:12-13; Psalms 18:48-49. As applicable to the Redeemer, it means that he would make the name of God known to people, or that “through him” that name would be made known.
Unto my brethren - Compare John 20:17; Romans 8:29. The word “brethren” would embrace literally brothers; kinsfolk; countrymen; then, those of the same opinion, profession, or religion; then, in a still larger sense, the human race as descended from a common parent. As having reference to the Redeemer, it would embrace here not only those who were his immediate followers and whom he called brethren - not only those of his own nation, - but the human family in general, toward whom he consented to sustain this relation. Compare the notes at Hebrews 2:10-12, where this passage is quoted and expressly applied to our Saviour.
In the midst of the congregation - Among the people assembled to worship there. See the notes at Hebrews 2:12. This is the place where praise is commonly celebrated, and he says that there he would make known the goodness of God. Compare Isaiah 38:19-20. It is not necessary to show that this was literally done by the Redeemer. It is enough to observe that this is the usual language of piety, and that the effect of his work has been to cause the praises of God to be celebrated in tens of thousands of the congregations of his saints.