1 Chronicles 11:2
And moreover in time past, even when Saul was king, thou wast he that leddest out and broughtest in Israel: and the LORD thy God said unto thee, Thou shalt feed my people Israel, and thou shalt be ruler over my people Israel. And moreover in time past, even when Saul was king, thou wast he that leddest out and broughtest in Israel: and the LORD thy God said unto thee, Thou shalt feed my people Israel, and thou shalt be ruler over my people Israel.
The tribes of Israel gathered to acknowledge David as their God-chosen king. Even in time past, while Saul was still king, David was the one who led Israel out and brought them in as leader of their forces. The Lord his God had appointed him to feed or shepherd His people Israel and to be ruler over them.