Deuteronomy 6:13-14 Thou shalt fear the Lord thy God, and serve him, and shalt swear by his name. Ye shall not go after other gods, of the gods of the people which are round about you.
Believers respond to grace by being God-fearers, people who believe God so firmly and love Him so fiercely that they naturally shy away from saying and doing anything that would grieve Him in any way. Paradoxically, fearing and loving are the same thing. It is faith that works. Such faith is worked in us by the Holy Spirit through the Gospel. We respond to it (to Jesus) by faith (fear). Jesus is so good and so strong that we can trust Him with all that we are.
The Gospel for Israel was the Salvation and Provision of God in the Exodus Event. Rehearse in your minds what great and good things the Lord did for you, and responding accordingly. The Gospel for us is the salvation and provision of God in the Christ Event, the death and resurrection of Christ. Rehearse it.
Then you will serve the Lord, and Him only, for He is your only Savior. God does not need our service, but other people do. We serve God by serving others. Serving is putting love into practice. It not theoretical; it is actually doing and saying things that make others feel better. We voluntary place ourselves under others as servants to meet their needs and lift them up. We treat others humans as if they were God, with such love, kindness, and respect. As Jesus says, “You have done it unto me.”