No Obligation

The secret things belong unto the LORD our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law. (Deuteronomy 29:29 KJV)

It is the glory of God to conceal things, but the glory of kings is to search things out. (Proverbs 25:2 ESV)

Samuel
The Lord said to Samuel, "How long are you going to grieve over Saul? I have rejected him as king over Israel. Fill your horn with oil and get going. I’m sending you to Jesse of Bethlehem because I have found my next king among his sons."
"How can I do that?" Samuel asked. "When Saul hears of it he’ll kill me!"
"Take a heifer with you," the Lord replied, "and say, 'I have come to make a sacrifice to the Lord.' Invite Jesse to the sacrifice, and I will make clear to you what you should do. You will anoint for me the person I point out to you." (1 Samuel 16:1-3 CEB)

God had no obligation to tell Saul Samuel's purpose in visiting Jesse of Bethlehem.