Psalms 68:31 - Matthew Poole's English Annotations on the Holy Bible

Egypt, Ethiopia: he names only these, as the great and ancient enemies of God, and of his people, and as a most wicked, and idolatrous, and incorrigible sort of men; see Jeremiah 13:23 Amos 9:7; but by them he synecdochically understands all other nations and people of the like character. Stretch out her hands unto God; either in way of humble supplication and submission, begging mercy of him; or to offer up the presents expressed, Psalms 68:29. But this prophecy, as also the next verse, evidently belongs to the times of the Messiah, when the Gentiles were tel be brought in to the knowledge and worship of the true God; with the thoughts and hopes whereof David oft comforteth himself in that confined and afflicted state of the church in his time.