Achish trusted David enough to have him as his personal body guard, and in this capacity he brought David and his men to the battlefield with the Philistines. The other Philistines refused to allow David to stay and insisted Achish send David away.
It is interesting to reflect on this chapter as the Philistines responded in the way I would have done in their place. They quoted from the victory songs after David killed Goliath in their argument with Achish. Yet Achish told David that he completely trusted him and apologised for sending him away. David must have been a very charismatic man as he had this ability to build complete loyalty from others, even men who should have been his enemy.
We know that David would never have attacked Saul, so perhaps David was playing a dangerous game at this time. He knew (either by pure common sense or because God told him) that the other Philistines would never trust him to fight alongside Achish, so he went along to the battlefield expecting to be sent home. In this way he did not damage his relationship with Achish, but he also did not have to fight Saul.
David seemed to be completely open and transparent most of the time and always with his men, yet political enough to lie to Achish about who he had raided each day. To be fair, David did not kill Philistines when he lived with Achish – perhaps because that would have been too difficult to hide?
I am looking forward to seeing how David’s relationship with Achish unfolds in the future when he is king of Isreal. David could be a man worth studying when considering how to live in our modern world without respect for God – he managed to be unrelenting in his faith and religion yet made friends and allies with many men through wisdom which I conclude came from God.