Adam Clarke on Psalms 43:5

Why art thou cast down - Though our deliverance be delayed, God has not forgotten to be gracious. The vision, the prophetic declaration relative to our captivity, was for an appointed time. Though it appear to tarry, we must wait for it. In the end it will come, and will not tarry; why then should we be discouraged? Let us still continue to trust in God, for we shall yet praise him for the fullest proofs of his approbation in a great outpouring of his benedictions.