1 Samuel 10:17

And Samuel called the people together unto the LORD to Mizpeh;

Samuel called Israel together before the Lord at Mizpeh at the time of their demand for a king. The gathering was convened to address the people about that demand and to make God's choice of king publicly known. The people prayed and sought divine guidance there in a public ceremony.

Samuel reminded them that God had rescued them from Egypt and from later oppressors, yet they had rejected God as their ruler and asked for human authority. To choose kingship in place of God's rule was a serious sin and a mistake, driven by the appeal of the customs and royal display of the nations around them.

Then lots were cast and successively identified the tribe, then the family, then the household, revealing Saul as the man God had chosen to be king. Saul's earlier anointing had not yet been made known to the nation, so the lot served to confirm the choice publicly. Conscious of and overcome by the weight of responsibility, Saul had withdrawn from the assembly and was not present when he was selected, and he had to be brought back before the people.