David's Loyalty to Saul

We often stress (rightfully) David's loyalty to Saul, God's anointed, even when Saul is obviously out of his mind and what we might consider "unfit for office". David's patience and reluctance to harm Saul in any way are great lessons to learn about submission to tyrants and patience in adversity.

But it should not be forgotten that David was also eager to enlist his help to the Philistines when they gathered together to do battle with Saul and his sons. Providentially, David is delivered from what could have been a very interesting battle, when the other Philistine lords question Achish and disallow David to go with them. But David's willingness and eagerness to be involved in the battle seem to indicate that David would have been very willing to fight for and with the Philistines, even (one speculates) to the point of killing Saul.

David's loyalty is not an absolute loyalty that would always prevent him from killing God's anointed. He recognizes that in one situation he is seizing for the throne and refusing to place his trust in God's word (the promise that he would become king after Saul). Furthermore, any sort of vigilante assassination would have been a great blemish on his record with the people of Israel. In the other situation, joining forces with the Philistines, God is providentially delivering up the throne to David. As it turns out that is exactly what God does, but He does it completely without David with the swords of the Philistines and ultimately Saul's own hand.
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6/24 Update

After some further consideration and tossing the idea around to others, I'm not persuaded that the above is the best interpretation of David's seeming willingness to fight with the Philistines. I'm still a little puzzled by the record of David's eagerness to fight, but I think given chs. 24, 26 and David's Song of the Bow lamenting Saul's death, it seems unlikely that David was really willing to fight Israel, much less kill Saul. I'll leave this post up, but that's what I'm thinking as of now.