In verses 14 through 23 we see that the anointing of David was confirmed also from the negative side.
Verse 14 says that the Spirit of Jehovah departed from Saul and that an evil spirit from Jehovah terrorized him. That was a further confirmation that God had chosen someone other than him. From that time onward Saul no longer had any peace, and he became jealous of David. The more he saw the good points of David, the more he realized that the kingdom would not go to his son Jonathan but to David. Therefore, Saul tried to kill David a number of times. On the one hand, Saul was terrorized by an evil spirit. On the other hand, he was troubled by his realization concerning David. Saul realized that the kingdom would not be a monarchy passed on to Jonathan but instead would go to David.
When Saul's servants saw that an evil spirit from God was terrorizing him, they suggested that they seek out a man who was skilled in playing the lyre and who could play it when the evil spirit was upon Saul. Saul agreed, and David was brought to Saul to serve as his attendant. David played the lyre to refresh Saul at home (v. 23), and he also became Saul's armor bearer (v. 21c). Saul loved him greatly.
Under God's sovereignty, David was selected to become an attendant of Saul. God put these two together to live and work together very closely. Eventually, however, the closer they became, the more Saul hated David. Saul and David became a test to each other. Simply by being put together, these two were fully tested. Saul was exposed as a person who was opposite to God's will, and David was manifested to be a man according to God's heart. This was God's sovereignty.
For David to be tested in his relationship with Saul meant that David was continually put on the cross. This may also be our experience in the church life and in our married life. The saints in the church life, especially the elders, may become a test, a cross, to us. Likewise, in married life our spouse will be a cross to us. Since there should be neither divorce nor separation, the only way for us in our married life is to go to the cross and remain there, allowing the cross to terminate our flesh and our particular kind of ambition.