He has made everything beautiful in its time. (Ecc. 3:11)
David had a marvelous promise, but David could not bring his own promise to pass. Only the One who had made the promise could bring about the promise and, at the same time, make the man ready to step into its fullness.
God was gradually teaching him how to be a captain of men, showing him that he must inquire of the Lord, and even using the wisdom of others to keep him from tainting his prophesied kingly office. David also realized that even if he had opportunity, he must not force things in order to foreshorten his wait. His throne must be established in righteousness, not by blood.
For all his frailties, David succeeded marvelously in this, so detaching his prophecy from his personal conflict with Saul that he was able in all sincerity to write a touching song of lament at the slain king’s death.
He learned the great lesson of entrusting himself to God for the outworking of his calling, expressed cleverly by Abigail as she referenced David’s most famous God-given victory:
Yet a man has risen to pursue you and seek your life, but the life of my lord shall be bound in the bundle of the living with the LORD your God; and the lives of your enemies He shall sling out, as from the pocket of a sling. (1 Sam. 25:29)
Through many trials David would take the throne, but in God’s own way and timing. By his own hand, David could not have achieved this – he could only have marred it.