Serve one another humbly in love. For the entire law is fulfilled in keeping this one command: “Love your neighbor as yourself (Galatians 5:13,14).
Martin Luther comments on being a neighbor to everyone
Although I am an unworthy and condemned man, my God has given me in Christ all the riches of righteousness and salvation without any merit on my part, out of pure, free mercy, so that from now on I need nothing except faith which believes that this is true. Why should I not, therefore, freely, joyfully, with all my heart, and with an eager will do all things which I know are pleasing and acceptable to such a Father who has overwhelmed me with his inestimable riches?
I will, therefore, give myself as a Christ to my neighbor, just as Christ offered himself to me. I will do nothing in this life except what I see is necessary, profitable, and salutary to my neighbor, since through faith I have an abundance of all good things in Christ.
Behold, from faith thus flow forth love and joy in the Lord. And from love [flows] a joyful, willing, and free mind that serves one’s neighbor.…
Therefore, if we recognize the great and precious things which are given us, as Paul says [Romans 5:5] , our hearts will be filled by the Holy Spirit with the love which makes us free, joyful, almighty workers, and conquerors over all tribulations, servants of our neighbors, and yet lords of all.…
Just as our neighbor is in need and lacks that in which we abound, so we were in need before God and lacked his mercy. Hence, as our heavenly Father has in Christ freely come to our aid, we also ought freely to help our neighbor through our body and its works. Each one should become, as it were, a Christ to the other that we may be Christs to one another and Christ may be the same in all, that is, that we may be truly Christians.