"“And it came to pass in those days, that the Philistines gathered their armies together for warfare, to fight with Israel. And Achish said unto David, Know thou assuredly, that thou shalt go out with me to battle, thou and thy men.” David had no intention of lifting his hand against his people; but he was not certain as to what course he would pursue, until circumstances should indicate his duty. He answered the king evasively, and said, “Surely thou shalt know what thy servant can do.” Achish understood these words as a promise of assistance in the approaching war, and pledged his word to bestow upon David great honor, and give him a high position at the Philistine court. PP 674.1"
"Now the Philistines gathered together all their armies to Aphek: and the Israelites pitched by a fountain which is in Jezreel."
The EGW passage directly quotes and expands upon the events described in 1 Samuel 29:1, focusing on Achish's request for David's participation in the war against Israel and David's ambiguous response.
"He reviewed the great mercy of God in preserving him from the hand of Saul, and determined not to betray a sacred trust. Even though the king of Israel had sought his life, he would not join his forces with the enemies of his people. PP 674.2"
"And he said unto his men, The Lord forbid that I should do this thing unto my master, the Lord’s anointed, to stretch forth mine hand against him, seeing he is the anointed of the Lord."
The EGW passage describes David's refusal to harm Saul, echoing the sentiment expressed in 1 Samuel 24:6 where David says he would not stretch forth his hand against the Lord's anointed. The passage amplifies the principle of respecting God's anointed, even when wronged.