Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
But David, after all, is only a man; and immediately after this testimony that God was with him (a testimony that even Saul acknowledged), his faith fails, and he passes over into the midst of the enemies of God's people. God, no doubt, makes use of this means to remove David from peril. But at the same time, he is tried and chastened, and is exposed to the dreadful necessity of appearing ready to fight against Israel. There is but One whose perfection and wisdom were His safeguard in every trial. We may remark that it was immediately after an evident interposition of God (Sa1 26:12) that David's faith fails. It is the same with Elijah (1 Kings 19). One would say that, in our hearts, faith exhausts itself by an unusual effort. Faith may carry us through the crisis; but the heart, which was the vessel of faith, is terrified by it; whilst in Jesus we find an equability of perfection altogether divine.
David removes to a distance from the royal city. In the land of the Philistines he gains their king's favour, not by faith, but by a prudence inconsistent with truth. It is an unhappy position; nevertheless, God does not forsake him. He chastises him, and in a painful manner, but He spares and preserves him. We have seen similar ways of the Lord in the case of the fugitive Jacob. Achish, who knows David, wishes to employ him in his service, and David cannot refuse; for when he who possesses the energy which the Spirit of God imparts by faith, has placed himself in a false position through unfaithfulness, he has no power against the one under whose authority he has placed himself; and if he does not use the energy with which he is endowed in favour of his protector, he very naturally excites his jealousy. He would have avoided all this by going to Ziklag, but he could not. God in His mercy preserved David, but he was now in a sad and false position.