Psalms 77:15

15.Thou hast redeemed thy people by thy arm. The Psalmist here celebrates, above all the other wonderful works of God, the redemption of the chosen people, to which the Holy Spirit everywhere throughout the Scriptures invites the attention of true believers, in order to encourage them to cherish the hope of their salvation. It is well known that the power of God was at that time manifested to the Gentiles. The truth of history, indeed, through the artifice of Satan, was corrupted and falsified by many fables; but this is to be imputed to the wickedness of those in whose sight those wonderful works were wrought, who, although they saw them, chose rather to blind their eyes and disguise the truth of their existence, than to preserve the true knowledge of them. (301) How can we explain the fact that they made Moses to be I know not what kind of a magician or enchanter, and invented so many strange and monstrous stories, which Josephus has collected together in his work against Apion, but upon the principle that it was their deliberate purpose to bury in forgetfulness the power of God? It is not, however, so much the design of the prophet to condemn the Gentiles of the sin of ingratitude, as to furnish himself and others of the children of God matter of hope as to their own circumstances; for at the time referred to, God openly exhibited for the benefit of all future ages a proof of his love towards his chosen people. The word arm is here put metaphorically for power of an extraordinary character, and which is worthy of remembrance. God did not deliver his ancient people secretly and in an ordinary way, but openly, and, as it were, with his arm stretched forth. The prophet, by calling the chosen tribes the sons of Jacob and Joseph, assigns the reason why God accounted them as his people. The reason is, because of the covenant into which he entered with their godly ancestors. The two tribes which descended from the two sons of Joseph derived their origin from Jacob as well as the rest; but the name of Joseph is expressed to put honor upon him, by whose instrumentality the whole race of Abraham were preserved in safety. (302)