The Lord had miraculously and faithfully proven His Personal provision to Israel, but after the Red Sea, they started to complain and doubt Him. When the Amalekites attacked them, Moses relied on God's power to give them victory, utilizing the support of others. When Israel won because of the Lord's help, Moses built an altar called "The Lord is my Banner". indicating their humble confidence in Him, and seeking His leadership, protection and victory going forward.  Video of this service is also available:  https://www.youtube.com/watch?v=itqWo65r-tE&t=1265s