1 Samuel is a history book in the Old Testament of the Bible. This book teaches us that we must always obey God.
1 Samuel tells the story of the first king of Israel. For many centuries, Israel had no kings. The people did whatever they wanted to do. But God appointed special judges to lead the people.
The last of these special judges was Samuel (1 Samuel 7:15). Samuel was a very holy man.
When Samuel was old, the people asked Samuel to appoint a king (1 Samuel 8). God told Samuel to appoint Saul. Saul sometimes obeyed God. But sometimes, Saul was evil.
So, God chose David to be king instead of Saul (1 Samuel 16). David trusted God. We see this when David fought Goliath (1 Samuel 17). And David loved God. But David did not become king immediately. Saul was still the king. David respected Saul. David even refused to attack Saul. The book of 1 Samuel ends with the story of Saul's death.