The hatred of the king towards him increased daily, under the influence of jealousy, for the wicked always persecute the good. He, therefore, commanded his servants and Jonathan his son, to prepare snares against his life. But Jonathan had even from the first had a great regard and affection for David; and therefore the king, being taken to task by his son, suppressed the cruel order he had given. But the wicked are not long good. For, when Saul was afflicted by a spirit of error, and David stood by him, soothing him with the harp under his trouble, Saul tried to pierce him with a spear, and would have done so, had not he rapidly evaded the deadly blow.
From this time forth, the king no longer secretly but openly sought to compass his death; and David no longer trusted himself in his power. He fled, and first betook himself to Samuel, then to Abimelech, and finally fled to the king of Moab. By-and-by, under the instructions of the prophet Gad, he returned into the land of Judah, and there ran in danger of his life. At that time, Saul slew Abimelech the priest because he had received David; and when none of the king's servants ventured to lay hands upon the priest, Doeg, the Syrian, fulfilled the cruel duty.
After that, David made for the desert. Thither Saul also followed him, but his efforts at his destruction were in vain, for God protected him. There was a cave in the desert, opening with a vast recess. David had thrown himself into the inner parts of this cave. Saul, not knowing that he was there, had gone into it for the purpose of taking bodily refreshment, and there, overcome by sleep, he was resting. When David perceived this, although all urged him to avail himself of the opportunity, he abstained from slaying the king, and simply took away his mantle.
Presently going out, he addressed the king from a safe position behind, recounting the services he had done him, how often he had exposed his life to peril for the sake of the kingdom, and how last of all, he had not, on the present occasion, sought to kill him when he was given over to him by God. Upon hearing these things, Saul confessed his fault, entreated pardon, shed tears, extolled the piety of David, and blamed his own wickedness, while he addressed David as king and son.
He was so much changed from his former ferocious character, that no one could now have thought he would make any further attempt against his son-in-law. But David, who had thoroughly tested and known his evil disposition, did not think it safe to put himself in the power of the king, and kept himself within the desert. Saul, almost mad with rage, because he was unable to capture his son-in-law, gave in marriage to one Faltim his daughter Melchol, who, as we have related above, had been married to David. David fled to the Philistines.
Source: Sacred History (New Advent)