Psalms 40:9

I have preached righteousness - I think it best to refer these words to Christ and his apostles. In consequence of his having become a sacrifice for sin, the Jewish sacrificial system being ended, the middle wall of partition was broken down, and the door of faith, the doctrine of justification by faith, opened to the Gentiles. Hence the Gospel was preached in all the world, and the mercy of God made known to the Gentiles; and thus righteousness - justification by faith, was preached in the great congregation - to Jews and Gentiles, throughout the Roman empire.

The great congregation, both in this and the following verse, I think, means the Gentiles, contradistinguished from the Jews.

The word righteousness means the plan or method of salvation by Jesus Christ - God's method of justifying sinners by faith, without the deeds of the law. See Romans 3:25-26 (note), and the notes there.

I have preached righteousness in the great congregation - I have main tained and defended the principles of righteousness and truth among assembled multitudes. it would be difficult to see how this could be applied to David himself, or on what occasion of his life this could be said of him; but no one can doubt that this is applicable to the Messiah:

(a) He was a preacher.

(b) He addressed vast multitudes.

(c) Before them all, and at all times, he maintained and illustrated the great principles of "righteousness" as demanded by the law of God, and unfolded the way in which all those multitudes might become righteous before God.

Lo, I have not refrained my lips - I have not closed my lips. I have not kept back the truth.

O Lord, thou knowest - He could make this solemn appeal to God as the Searcher of hearts, in proof that he had faithfully uttered all that had been required of him in making known the will of God. Compare John 17:4, John 17:6,John 17:8, John 17:14, John 17:26.

40:9 Righteousness - Thy faithfulness. Great congregation - In the most public and solemn assemblies: not only to the Jews, but also to all nations; to whom Christ preached by his apostles, as is observed Ephesians 2:17 .Not refrained - From preaching it, even to the face of mine enemies.