Charles Ellicott Commentary 1 Samuel 16:2

"And Samuel said, How can I go? if Saul hear it, he will kill me. And Jehovah said, Take a heifer with thee, and say, I am come to sacrifice to Jehovah." — 1 Samuel 16:2 (ASV)

He will kill me. —The unhappy mental malady of Saul must have made rapid progress. The jealous king was indeed changed from the Saul who, even in his self-willed rebellion against the Lord, was careful to pay honour to Samuel. But now the aged prophet felt that if he crossed the king’s path in any way, even in carrying out the commands of the invisible King of Israel, his life would be forfeited to the fierce anger of Saul.

Take an heifer with you. —And the Divine voice instructed Samuel how he should proceed. There was to be as yet no public anointing of the successor to Saul; only the future king must be sought out, and quietly, but solemnly, set apart for service before the Lord, and then watched over and carefully trained for his high office.