As soon as Saul saw David go out against the Philistine, he said to Abner, the commander of the army, “Abner, whose son is this youth?” And Abner said, “As your soul lives, O king, I do not know.” And the king said, “Inquire whose son the boy is.” And as soon as David returned from the striking down of the Philistine, Abner took him, and brought him before Saul with the head of the Philistine in his hand. And Saul said to him, “Whose son are you, young man?” And David answered, “I am the son of your servant Jesse the Bethlehemite.” (1 Samuel 17:55-58)
Saul inquires whose son David is, because the relationship has become more intimate, and David now needs to become family. The defeat of Goliath has earned David a place in Saul's immediate household, and we see soon that Saul gives one of his daughters to David as a wife. Notice the difference in the Saul/David relationship from before the Goliath battle:
Now the Spirit of the Lord departed from Saul, and a harmful spirit from the Lord tormented him. And Saul's servants said to him, “Behold now, a harmful spirit from God is tormenting you. Let our lord now command your servants who are before you to seek out a man who is skillful in playing the lyre, and when the harmful spirit from God is upon you, he will play it, and you will be well.” So Saul said to his servants, “Provide for me a man who can play well and bring him to me.” One of the young men answered, “Behold, I have seen a son of Jesse the Bethlehemite, who is skillful in playing, a man of valor, a man of war, prudent in speech, and a man of good presence, and the Lord is with him.” Therefore Saul sent messengers to Jesse and said, “Send me David your son, who is with the sheep.” And Jesse took a donkey laden with bread and a skin of wine and a young goat and sent them by David his son to Saul. And David came to Saul and entered his service. And Saul loved him greatly, and he became his armor-bearer. And Saul sent to Jesse, saying, “Let David remain in my service, for he has found favor in my sight.” And whenever the harmful spirit from God was upon Saul, David took the lyre and played it with his hand. So Saul was refreshed and was well, and the harmful spirit departed from him. (1 Samuel 16:14-23)
Saul loved David greatly before, but only in as much as David would send the evil spirit away from him. Remember, Saul no longer has the Holy Spirit, and so he is outside the church, although he is the visual head of Israel, and so David is very valuable to him in what he can accomplish for him. David can ward off demons, and he is also Saul's armor bearer. He is like a ward of protection. Even though Saul loves David, only after the defeat of Goliath does Saul intend to change the relationship into something more. Saul is putting a deeper faith in David. Before, he was putting faith in the miracles that David wrought for him, and now he is...doing the same thing. He's putting faith in David as his champion, defeating not only demons but the devil himself, and this is still faith in the miraculous work of David. Saul, being king himself, still refuses to put his faith in David as king over him. And he never will. Remember, God has already anointed David as the true king of Israel, so David is king, just as Christ is the messiah and all is his, and yet many today--a majority--refuse to bend the knee to their rightful king. Most people are their own kings, and they don't need Christ. They will not put faith in Jesus as their Lord and savior, and yet many who call themselves Christian will put their faith only in his miracles.
According to Zacharias Ursinus, in his commentary on the Heidelberg Catechism, the scriptures speak of four kinds of faith. Only the last, justifying faith, saves us. Here are the other three:
Historical faith. This is believing the word of God is true, that the Bible isn't just a made-up thing but an historical text, and that the doctrines found within are true. Does this save us? No. Remember the devils believed and trembled. Simon Magus also believed.
Temporary faith. This is just like historical faith, except it is accompanied by joy. However, this faith does not endure. "As for what was sown on rocky ground, this is the one who hears the word and immediately receives it with joy, yet he has no root in himself, but endures for a while, and when tribulation or persecution arises on account of the word, immediately he falls away." (Matthew 13:20-21)
The faith of miracles. This is having faith in the works of God for our temporal benefit. Paul writes in 1 Corinthians 13, "And if I have prophetic powers, and understand all mysteries and all knowledge, and if I have all faith, so as to remove mountains, but have not love, I am nothing." If he has the power of God in his hands, but he does not have the love that God bestowed on us through his sacrificial death on the cross, he is still dead in his sins, and so are we, if we have put our faith in the wonders of God and not the atoning death of Christ on our behalf. The sons of Sceva and Simon Magus sought this power, and yet they were not saved. Most importantly, read this passage from Luke:
And he called the twelve together and gave them power and authority over all demons and to cure diseases, and he sent them out to proclaim the kingdom of God and to heal. And he said to them, “Take nothing for your journey, no staff, nor bag, nor bread, nor money; and do not have two tunics. And whatever house you enter, stay there, and from there depart. And wherever they do not receive you, when you leave that town shake off the dust from your feet as a testimony against them.” And they departed and went through the villages, preaching the gospel and healing everywhere. (Luke 9:1-6)
Who is included in the twelve? Judas! Judas, as an apostle, performed miracles with the rest of them, but Christ called him a devil. Many will say at the end of the age, "Lord, did I not cast out devils in your name?" to whom he will reply, "I never knew you."
Justifying faith alone contains the belief that the "righteousness of Christ is granted and imputed to us, so that we are accounted just in the sight of God." (110-111). Another thing that Ursinas claims that I found fascinating is that only those who possess a justifying faith know what it is, just as one cannot understand the flavor of honey unless he tastes it himself, no matter how much the flavor has been described to him beforehand.
So, we see that Saul has not applied David's "salvation" to himself by submission. He has only brought David closer in order to utilize this powerful person whom God has chosen. Likewise, we can have faith in the power of God without submitting ourselves in penitence and obedience to the Lord's will. We can believe that the scriptures are true, assent to them, and call upon God's power, but without the love of Christ in his atoning sacrifice, we are empty of salvation. Make Jesus Christ your king.
