The Lord said to Samuel, “How long will you mourn for Saul, since I have rejected him as king over Israel? Fill your horn with oil and be on your way; I am sending you to Jesse of Bethlehem. I have chosen one of his sons to be king.”— 1 Samuel 16:1 NIV
Why do you and I keep crying over spilled milk?

God gave instructions to Saul as he prepared for battle against the Amalekites; remembering what they had done to Israel when they waylaid the Israelites as they came out of Egypt. Thus, God instructs Saul to destroy the Amalekites: “Now go, attack the Amalekites, and destroy everything that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels, and donkeys.” However, Saul disobeyed God and spared the Amalekite King Agag and the best of their sheep, cattle, and lambs.
Saul lied and said that he had carried out the Lord’s commands to the fullest. In response to Saul’s lie, Samuel replies in 1 Samuel 15:14: “What is this bleating of sheep and lowing of cattle that I hear?” Saul thought he could fool Samuel: but he disrespected the omniscience of God as well as the prophetic office of Samuel. This disrespect necessitates God’s rejection of Saul as king, and Samuel laments his decision in making Saul king of Israel.
God cornered Samuel and told him that he has mourned long enough, and it is time for him to “stop crying over spilled milk”! Samuel mourned over Saul, and we understand. We have grieved over a relationship that is dead with no hope of resurrection. We have been depressed over a missed opportunity. We have mourned over an unrealized expectation. We have cried over a moral or ethical failure. Whether we like it or not, there are some people, circumstances, and situations we must learn to get over. Regardless of how much one loves, cares, or yearns for someone or something, God declares that there comes a day when one must stop crying over spilled milk! It’s time to get over it! It’s time to move on!
Why does God tell Samuel to stop mourning? Why does God demand that one stop crying over spilled milk? The first reason ought to be self-explanatory: By continuing to grieve and mourn over Saul, Samuel is growing derelict in his responsibilities as priest, judge, and prophet. He is God’s prophet. He is the spiritual leader among the people. He is the proclaimer of the Good News. He is the priest anointed to do the Lord’s work. To continue mourning over Saul suggests that Samuel is abdicating his spiritual assignment. He is one who can see and foretell God’s future. However, if he mourns over Saul, he is solely focused on the past. God admonished Samuel to cease mourning over Saul because persistent grieving would change his nature and not the situation.