O my God! I have put my trust in thee. By this verse we learn, (what will appear more clearly afterwards,) that David had to do with men; but as he was persuaded that his enemies were, as it were, the scourges of God, he with good reason asks that God would restrain them by his power, lest they should become more insolent, and continue, to exceed all bounds. By the word trust he confirms what he had just said of the lifting up of his soul to God; for the term is employed either as descriptive of the way in which the souls of the faithful are lifted up, or else faith and hope are added as the cause of such an effect, namely, the lifting up of the soul. And, indeed, these are the wings by which our souls, rising above this world, are lifted up to God. David, then, was carried upward to God with the whole desire of his heart, because, trusting to his promises, he thereby hoped for sure salvation. When he asks that God would not suffer him to be put to shame, he offers up a prayer which is taken from the ordinary doctrine of Scripture, namely, that they who trust in God shall never be ashamed. The reason which is added, and which he here pleads, to induce God to have pity upon him, ought also to be noticed. It is this, that he might not be exposed to the derision of his enemies, whose pride is no less hurtful to the feelings of the godly than it is displeasing to God.

O my God, I trust in thee - This is the first thought - a feeling that he had true confidence in God, and that in all the duties of life, in all his trials, and in all his hopes for the future, his reliance was on God alone.
Let me not be ashamed - That is, let me never be so forsaken by thee as to have occasion for shame that I have thus trusted in thee. The prayer is not that he might never be ashamed to avow and confess his trust in God, but that he might "find" God to be such a helper and friend that he might never be ashamed on account of the trust which he had put in Him, as if it had been a false reliance; that he might not be disappointed, and made to feel that he had done a foolish thing in confiding in One who was not able to help him. See the word explained in the notes at Job 6:20. Compare Isaiah 30:5; Jeremiah 8:9; Jeremiah 14:3-4.
Let not mine enemies triumph over me - This explains what the psalmist meant by his prayer that he might not be "ashamed," or put to shame. He prayed that he might not be vanquished by his foes, and that it might not appear that he had trusted in a Being who was unable to defend him. Applied now to us, the prayer would imply a desire that we may not be so overcome by our spiritual foes as to bring dishonor on ourselves and on the cause which we profess to love; that we may not be held up to the world as those who are unable to maintain the warfare of faith, and exposed to scorn as those who are unfaithful to their trust; that we may not be so forsaken, so left to trial without consolation, so given over to sadness, melancholy, or despair, as to leave the world to say that reliance on God is vain, and that there is no advantage in being his friends.

I trust in thee - I depend upon thy infinite goodness and mercy for my support and salvation.
Let me not be ashamed - Hide my iniquity, and forgive my guilt.

O my God, I (b) trust in thee: let me not be ashamed, let not mine enemies triumph over me.
(b) That you will take away my enemies, which are your rods.

O my God, I trust in thee,.... He claims his interest in God, and expresses his faith and confidence in him, in the midst of all his troubles; See Gill on Psalm 7:1;
let me not be ashamed; meaning of his trust in God, by being disappointed of the help, deliverance, and salvation from him, which he trusted in him for; and the believer, as he has no reason to be ashamed of God, the object of his trust; so neither of the act of his hope or trust in him; nor shall he; for hope makes not ashamed; see Psalm 119:116, Romans 5:5;
let not mine enemies triumph over me; either his temporal enemies, his subjects that were risen up against him; or his spiritual enemies, Satan, and the men of the world, who rejoice and triumph when the saints are forsaken by God; and they are ready to say, as David's enemies did of him, there is no help or salvation for him in God, Psalm 3:2; and when they fall into their hands, or fall by them.

not be ashamed--by disappointment of hopes of relief.

Ashamed - Disappointed of my hope.