The Greek word allelon (αλληλων) provides us with a helpful introduction as to the ways in which Christians ought to serve one another. How? Because this word means "one another" or "each other." It is frequently used to describe our mutual obligations, those responsibilities that all members of the body of Christ have toward each other.
In Christ, we belong to each other and form one body (Romans 12:5). We are members of one another (Ephesians 4:25). "We have fellowship with one another" (1 John 1:7). Paul prayed that the Roman Christians would have "the same mind with one another according to Christ Jesus" (Romans 15:5). To avoid division in the body, Paul desired members to "have the same care for one another" (1 Corinthians 12:25). "Be hospitable to one another" (1 Peter 4:9).
Perhaps the most comprehensive command ever given by Jesus was the well-known "Love one another" (John 13:34). "A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another. By this all men will know that you are My disciples, if you have love for one another" (vv. 34-35). Love is the sine qua non (without which there is nothing) of the family of God. This command is of such a fundamental foundation to our Christian duty that it is repeated again in John 15:12, 17; Romans 13:8; 1 Thessalonians 4:9; 1 Peter 1:22; 1 John 3:11, 23; 4:7, 11-12; and 2 John 5. This is the attitude that Christians ought to have toward each other, and how we ought to interact with one another.
Paul built on this command further: "Be devoted to one another in brotherly love; give preference to one another in honor" (Romans 12:10). "Through love serve one another. For the whole Law is fulfilled in one word, in the statement, 'YOU SHALL LOVE YOUR NEIGHBOR AS YOURSELF'" (Galatians 5:13). He prayed that the Lord would help the Thessalonians' love to increase not only for each other, but also that their love would increase for everyone else (1 Thessalonians 3:12). "See that no one repays another with evil for evil, but always seek after that which is good for one another and for all men" (1 Thessalonians 5:15). In his second letter to the Thessalonians, he thanked God that their mutual love was indeed increasing (2 Thessalonians 1:3). His exhortation to local churches never varies: "Put on love, which is the perfect bond of unity" (Colossians 3:14).
As noted in the third paragraph above, both the apostle John and apostle Peter echo this command (1 John 3:11; 4:7; 1 Peter 1:22). Examples of how this love works out in practice are numerous: "Bear one another's burdens, and thus fulfill the law of Christ" (Galatians 6:2). "Do not merely look out for your own personal interests, but also for the interests of others. Have this attitude in yourselves which was also in Christ Jesus" (Philippians 2:4-5). "And be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you" (Ephesians 4:32). "Rejoice with those who rejoice, and weep with those who weep. Be of the same mind toward one another; do not be haughty in mind, but associate with the lowly. Do not be wise in your own estimation" (Romans 12:15-16). Christ's love is a love that surpasses knowledge (Ephesians 3:19).
One of the ways in which Christ's love manifests itself within us is through acceptance and forgiveness. "Let us not judge one another anymore" (Romans 14:13). "Accept one another, just as Christ also accepted us" (Romans 15:7). "Bearing with one another, and forgiving each other, whoever has a complaint against anyone; just as the Lord forgave you, so also should you" (Colossians 3:13). "Be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you" (Ephesians 4:32). "Confess your sins to one another, and pray for one another" (James 5:16).
Through acceptance and forgiveness, you achieve peace. "Be at peace with one another" (Mark 9:50). "Live in peace with one another" (1 Thessalonians 5:13*). "Be of the same mind toward one another" (Romans 12:16a). Paul explains how this can be done: "do not be haughty" (Romans 12:16b). "With all humility and gentleness, with patience, showing forbearance to one another in love" (Ephesians 4:2). "Do nothing from selfishness or empty conceit, but with humility of mind let each of you regard one another as more important than himself" (Philippians 2:3). "Clothe yourselves with humility toward one another" (1 Peter 5:5).
Another way in which Christ's love manifests itself within is is through service. "Through love serve one another" (Galatians 5:13). Peter says something similar: "As each one has received a special gift, employ it in serving one another" (1 Peter 4:10*). Jesus had taught the same lesson when He told His disciples to "wash one another's feet" (John 13:14). "Be subject to one another in the fear of Christ" (Ephesians 5:21). "Bear one another's burdens, and thus fulfill the law of Christ" (Galatians 6:2).
Paul desired that the Roman Christians would be mutually encouraged by each other's faith (Romans 1:12). One of the purposes of our gathering together for fellowship on Sundays is to "spur one another to love and good deeds . . . encouraging one another" (Hebrews 10:24-25). "Encourage one another day after day" (Hebrws 3:13*). "Comfort one another . . . encourage one another, and build up one another" (1 Thessalonians 4:18; 5:11). "Building yourselves up on your most holy faith" (Jude 20*).
Paul also desired mutual edification in the "building up of one another" (Romans 14:19). "Teaching and admonishing one another with psalms and hymns and spiritual songs" (Colossians 3:16*; Ephesians 5:19*). Paul was confident that the Roman Christians could "admonish one another" (Romans 15:14).
These are only some of the ways in which Christians can and should minister unto each other for the glory of God. There is much riding on the unity of the local church and it must be preserved with the utmost vigilance.
* The pronoun heautou (εαυτου) is used instead of allelon (αλληλων), but often has the same meaning.