But the king shall rejoice in God - This passage, as was remarked in the Introduction to the psalm, shows that this psalm could not have been composed in the time of Saul, since the title king was not then given to David. The use of the term here in the third person does not prove that the psalm could not have been written by David himself, for he may have spoken of himself simply as “the king,” and all the more forcibly and properly as he was driven unjustly from his throne, and was now an exile, yet was still a king - the king. The title was his; the throne belonged to him, and not to Absalom who had driven him from it. It was not improper to allude to this fact in the manner in which it is referred to here, and to say that “the king” - the true, the real king - himself - should and would rejoice in God. He would find God to be his helper; and by God he would yet be restored to his throne.
Every one that sweareth by him shall glory - Everyone that sweareth to him, or maintains his oath of allegiance to him, shall be honored.
But the mouth of them that speak lies - All who have sworn falsely; all who have professed allegiance and have proved unfaithful; all those who, contrary to their oaths and their obligations, have been found in the rebellion. They shall not be permitted to exult or rejoice, but they shall be confounded and silenced. This expresses, therefore, the fullest confidence in God; the absolute belief of David that he would be again placed on his throne, and again permitted “to see the power and glory of God as” he had “seen it in the sanctuary” Psalms 63:2; the belief that he would be restored to prosperity, and that his enemies would be humbled and destroyed - So it will be with all who put their trust in God. There is certain joy and triumph for them, if not in this world, at least in the world to come.