The life and career of David are the subject of countless studies.  We are not going to rehash this material.  We will point out some of the differences between the character of Saul and that of David, and we will consider David's relations to non-Israelites.
         
Even at the end of his life, Samuel was still on a learning curve.  Here was a man who could read Saul's inmost thoughts and motives like an open book, but he was completely wrong about the choice of the next king.  He was all set to anoint the older brother Eliab.  It shows that, apart from the anointing of God, Samuel's natural thoughts were just as opinionated and error-prone as any man's.  He was not "holy" in himself.  God taught him (and us):  

 

         "The Lord does not look at the things man looks at.  Man looks at the outward appearance, but the Lord looks at the heart" (1 Sam 16:7).

 

This verse is a powerhouse of racial teaching.  Racialists of all stripes look for political leaders and spokesmen whose qualifications include a "proper" ethnicity.  They will support only the candidate who looks like them, or has a similar national background.  It is a cornerstone of Biblical racial teaching that such exterior attributes have nothing to do with suitability for leadership.

        

When David entered the room, the Spirit of God witnessed to Samuel that he was the one to anoint.  Samuel did so, no doubt to David's great shock and the astonishment of all his family, then
    
         the Spirit of the Lord came upon David in power (1 Sam 16:13).

​

As with Saul among the prophets, this must have been a tangible experience.  Also like Saul, God must have changed David's heart at this moment.  The connotation is that the Spirit of the Lord stayed with him, abiding in Him, from then on.  At the same time, the Spirit left Saul, to be replaced by "an evil spirit from the Lord" (1 Sam 16:14).