All these signs were fulfilled that day, Saul was anointed as king of Israel

1 Samuel 9:26-10:16
Go down ahead of me to Gilgal. I will surely come down to you to sacrifice burnt offerings and fellowship offerings, but you must wait seven days until I come to you and tell you what you are to do.”
As Saul turned to leave Samuel, God changed Saul’s heart, and all these signs were fulfilled that day.
When all those who had formerly known him saw him prophesying with the prophets, they asked each other, “What is this that has happened to the son of Kish? Is Saul also among the prophets?”
Saul replied, “He assured us that the donkeys had been found.” But he did not tell his uncle what Samuel had said about the kingship.
All Isreal knows the prophet, but not, apparently, this young provincial. The oil sets Saul apart for his high office. The detailed fulfilment of Samuel's predictions assures Saul of the prophet's authority. Saul goes home a new man.
Why?
Finally, Saul did not wait for the seven days until Samuel come.
What Samuel said are all fulfilled, for Samuel is a prophet of the Lord, what he said is like God's talk.
Saul is with the Spirit of the Lord so he was prophesying with the prophets. God was with Saul.
Saul was afraid to let his uncle know that Samuel has anointed him as a king of Israel. Maybe he is not ready for this new position in his heart.
How?
It is God's chosen on us so we can be someone and to do something. If there is not God's mercy and grace we will be in the dust and dead body.