John Gill Commentary 1 Samuel 16:3

"And call Jesse to the sacrifice, and I will show thee what thou shalt do: and thou shalt anoint unto me him whom I name unto thee." — 1 Samuel 16:3 (ASV)

And call Jesse to the sacrifice His family, both him and his sons, to partake of the peace offerings; as every offerer had a right to invite his friends, and whomsoever he pleased, to eat of those parts of them which belonged to him, as a feast before the Lord:

and I will show you what you will do ; when Jesse and his family were with him:

and you shall anoint to me him whom I name to you ; that is, anoint him to be king over Israel, whom he should point out so plainly to him, as if he called him by name.