Why did King Achish reject David in 1Sa 21 only to welcome him a few chapters later?

[tonychanyt]

David was vulnerable in 1 Samuel 21:

10 David rose and fled that day from Saul and went to Achish the king of Gath.

Gath was a Philistine city (1Sa 17:4), and Achish was a Philistine ruler. David was desperate. He was willing to seek refuge among his people's enemies to escape Saul, hoping to stay under Achish's protection.

11 But the servants of Achish said to him, “Is this not David, the king of the land? Did they not sing about him in their dances, saying: ‘Saul has slain his thousands, and David his tens of thousands’?”

Achish's servants alerted him that David was a servant of Saul and posed a danger. Achish didn't want him.

12 Now David took these words to heart and was very much afraid of Achish the king of Gath.

Why was David afraid?

David thought he was in danger now because he didn't have many men with him while fleeing from Saul. He was afraid that Achish would take revenge on David, who had killed many Philistines. Sensing that, David changed his tune:

13 So he changed his behavior before them and pretended to be insane in their hands and made marks on the doors of the gate and let his spittle run down his beard. 14 Then Achish said to his servants, “Behold, you see the man is mad. Why then have you brought him to me? 15 Do I lack madmen, that you have brought this fellow to behave as a madman in my presence? Shall this fellow come into my house?”

Achish was fooled by David's pretense and dismissed him.

Later, David wrote about this incident in (NIV) Psalm 34:

1 Of David. When he pretended to be insane before Abimelek, who drove him away, and he left.
I will extol the LORD at all times; his praise will always be on my lips.

David pretended to be insane before Achish and Abimelek. Wiki:

this seeming contradiction is easily explainable when you understand that Abimelech would have been his title and Achish, his actual name.

For the next many months, Saul continued to pursue David. Then, it was public knowledge that David was Saul's enemy. 1Sa 27:

2 David arose and went over, he and the six hundred men who were with him, to Achish the son of Maoch, king of Gath. 3 And David lived with Achish at Gath, he and his men, every man with his household, and David with his two wives, Ahinoam of Jezreel, and Abigail of Carmel, Nabal’s widow.

Why did King Achish reject David in 1Sa 21 only to welcome him in 1Sa 27?

Achish rejected David earlier, thinking that he was still Saul's servant. Later, the geopolitical situation changed. This time, David came with women and children, seeking asylum. Achish thought he could use David against Saul, their common enemy.

12 Achish trusted David, thinking, “He has made himself an utter stench to his people Israel; therefore he shall always be my servant.”

For the second time, Achish was fooled by David. David had an adventurous life.