1 Chronicles 22:8

Shed blood — Not that wars are simply unlawful, but to teach us that the church (whereof the temple was an illustrious type) should be built by Christ, the prince of peace, Isaiah 9:6, and that it should be gathered and built up, not by might or power but by God's spirit, Zechariah 4:6, and by the preaching the Gospel of peace. David therefore was less fit for that service, than one who had not been called to such bloody work. Likewise by setting him aside for this reason, God shewed how precious human life is to him.