One of the earliest church fathers to write in Latin was Tertullian, and he used the word sacramentum to refer to baptism and communion. The sacramentum was the oath a Roman soldier took when he joined the military.
Soldiers sign up once for service, and so do Christians—our baptism doesn’t wash off. So why have another sacrament? Why take communion, bread and wine, every week? Because soldiers and citizens continue to pledge allegiance. Husbands and wives repeat their love and enjoy their commitment. We are fickle and we need it, and God would nourish, strengthen and bless us in fellowship with Him every week.
But the Lord’s Supper is not just about our allegiance to God. It’s about His to us. The same night Jesus was betrayed He gave the disciples this meal. He knew they would be faithless and scattered, but told them that He would eat with them again in the kingdom of God. Even though they would be despairing the deserting, He would remain faithful to them.
God says the same thing to us. He pledges His covenant faithfulness to us here which is what our allegiance rests on. We don’t have faith in faith, faith in our perseverance. We have faith in Him, our risen Lord. So pledge yourself here to come, and welcome to Jesus Christ.