Verse 2. - For thou art the God of my strength; i.e. the God in whom is all my strength (Psalm 28:7). Why dost thou cast me off? An equivalent to the "Why hast thou forgotten me?" of Psalm 42:9. Why go I mourning because of the oppression of the enemy? Repeated, with the variation of a single word, from Psalm 42:9.

43:6-11 The way to forget our miseries, is to remember the God of our mercies. David saw troubles coming from God's wrath, and that discouraged him. But if one trouble follow hard after another, if all seem to combine for our ruin, let us remember they are all appointed and overruled by the Lord. David regards the Divine favour as the fountain of all the good he looked for. In the Saviour's name let us hope and pray. One word from him will calm every storm, and turn midnight darkness into the light of noon, the bitterest complaints into joyful praises. Our believing expectation of mercy must quicken our prayers for it. At length, is faith came off conqueror, by encouraging him to trust in the name of the Lord, and to stay himself upon his God. He adds, And my God; this thought enabled him to triumph over all his griefs and fears. Let us never think that the God of our life, and the Rock of our salvation, has forgotten us, if we have made his mercy, truth, and power, our refuge. Thus the psalmist strove against his despondency: at last his faith and hope obtained the victory. Let us learn to check all unbelieving doubts and fears. Apply the promise first to ourselves, and then plead it to God.For thou art the God of my strength,.... Who being the strong and mighty God was able to deliver and save him, as well as to plead his cause; and was the author and giver of strength, natural and spiritual, to him; and was the strength of his heart, life and salvation; and is a good reason why he committed his cause unto him;

why doest thou cast me off? this is the language of unbelief: it being what was not in reality, only in appearance: the psalmist was ready to conclude he was cast off and rejected of God, because he was afflicted and left in a desolate condition by him, and he did not immediately arise to his help and deliverance, and had withdrawn the light of his countenance from him; but God does not cast off or reject any of his people; they always continue in his love, and in his covenant, and in the hands of his Son; they are always in his sight and family, and shall never perish eternally; and whoever casts them off, or casts them out, he will not;

why go I mourning because of the oppression of the enemy? See Gill on Psalm 42:9.