Psalms 63:11

11. But… king “King,” according to the date given to the psalm, cannot here mean David, who never assumed that title during the life of Saul, though afterwards he thus spoke of himself in the third person, Psalms 21:1; Psalms 21:7; Psalms 61:6. It can, therefore, apply to none but Saul, and this eminently suits the unvarying tenor of David’s loyalty; his high conceptions of the theocracy; his marvellous reverence for Saul as the Lord’s anointed; his constant refusal to take Saul’s life, when in two instances he could have done it with a single stroke; his uniform distinction between Saul as rightful sovereign and those lying flatterers who led him astray; and the unaffected lamentation and inimitable elegy upon his death. It further illustrates his forgiving piety.

Every one that sweareth by him Whether the pronoun refers to “God,” or to “king,” in the preceding clause, may be grammatically indifferent; but it may be urged against the latter, and in favour of the former, that though in a heathen country it might pass as an allowable custom to swear by the king, (see Genesis 42:15,) the Hebrews were strictly forbidden to swear by any but God. Deuteronomy 6:13; Deuteronomy 10:20; Isaiah 65:16. What the prophet, Isaiah 45:23, calls “swearing,” the apostle, Romans 14:11, calls “confessing.” It was a religious acknowledgment of the supremacy of God.

But the mouth of them that speak lies This, with the preceding line, forms an antithetic parallelism, falsehood being opposed to truthful swearing in God’s name, and the rejoicing, or boasting in God to the shutting up the mouths of those who “speak lies.” This confirms the sense given of the passage.