Luke 1:74, 75 That he would grant unto us, that we being delivered out of the hand of our enemies might serve him without fear, in holiness and righteousness before him, all the days of our life.
Mary, through inspiration of the Holy Spirit, gives us the promise from her Son: Jesus will grant unto us the desire and ability to serve the Lord without fear. And we will serve Him in holiness and righteousness all the days of our life.
Jesus has come to deliver us from our spiritual enemies for a purpose: that we might serve the Lord. “We are saved by grace through faith for good works that we should walk in them.” We don’t serve God nor do good works naturally, so we must be transformed by grace to become what we were created to be: holy, righteous people that love and serve the Lord all of our days.
Martin Luther says in the Catechism that the Father gives, provides, and protects us out of goodness and mercy. And then, “For all this it my duty to thank and praise, serve and obey Him.” He also says that the Son is my Lord who has redeemed me from all sins, from death, and from the power of the devil, so that I may be his own and serve him in everlasting righteousness, innocence, and blessedness.
Luther also says that the Lord doesn’t need our service, but other people do. Therefore we serve the Lord by loving and serving others. This is the privilege and the promise: we want to love and serve people, and we get to do so without fear of our three spiritual enemies constantly harassing us.