Psalms 72:1

God is the source of all judgement (Deuteronomy 1:17); the king is His representative for administering it. May God therefore grant him such a knowledge of the divine laws and ordinances by which he is to govern Israel, and endow him with such a divine spirit of justice, as may make him a worthy ruler. Just judgement is the constant characteristic of the ideal king (Isaiah 11:3 ff; Isaiah 16:5; Isaiah 28:6; Isaiah 32:1). The words of this verse and the next are the echo of God's offer to Solomon, "Ask what I shall givethee;" and of Solomon's answer, "Give thy servant an understanding heart to judge thy people;" and a prayer for the effectual realisation of the promise, "Lo, I have given thee a wise and an understanding heart." (1 Kings 3:5 ff.).

the king … the king's son Not, to the king and his heir, for the Psalm speaks of but one ruler; but, to a king who is a king's son, the legitimate successor to the throne.