Saul became jealous of David after he killed Goliath the Philistine. David had become the nation's hero and it was clear God's favor and His spirit was upon David. Saul knew his reign was over but refused to relinquish authority under Samuel. He became paranoid about who would take his power from him and evil spirits plagued him. It was difficult for David to soothe Saul with the harp when he was seen as no threat; now David was seen by the king as an enemy.
Note two traits David exhibited in his service to God under Saul's leadership:
1. He did not become swayed by praise. As he returns to the palace with Saul, the women sing a tune giving credit to Saul for slaying thousands and to David for slaying tens of thousands, (1 Samuel 18:7). David did not let this praise go to his head. David had already been anointed King by Samuel, but he was content to wait for God's timing to assume his position as King. David knew that God's praise was more important than the people's. David simply continued to serve to the best of his ability.
2. David did not let Saul's hostility defeat him. David did not depend upon kind words or affirmations for his service. God would reward him in due time if he conducted himself well. He didn't storm out of the kings palace and go his way. He continued in faithful service even as his work was despised by the King. What a difficult place to be, yet sometimes God may even call us to serve in difficult circumstances so that He may receive greater glory.
Notice that God sends several special blessings in David's life. He is promoted (verse 5) and he has the companionship and deep affection of both Jonathan and Michal, Saul's son and daughter. Having good friends to support you as you face difficulty is a true blessing from God. Jonathan feels one in spirit with David not just brotherly love but a common service to God. So strong was the bond between them that they forged a covenant between them to watch over one another. Friendships like this are rare and should be treasured.
While Saul did not work to David's best interest, David did not use this as an excuse to return animosity or to avoid the King. He continued to serve Saul with all his might and trusted the Lord for his protection.
If you have been called to a place of difficult service, guard your mind that you do not become discouraged but commit yourself to serve the Lord well wherever he has placed you. Our reward is from the Lord and not from men.
May God richly bless you as you seek Him and as you serve Him.