I guess, the one anothers probably began in the book of Genesis, when Cain killed Abel, and God asked Cain 'Where is Abel, your brother?', to which Cain answered, "I do not know. Am I my brother's keeper?"
In the New Testament, we are to 'bear one another's burdens'. We are to 'love one another'. We are to 'exhort one another'. Some other 'one anothers' are to be kind to one another, comfort one another, serve one another, forgive one another, be at peace with one another, addressing one another with psalms, hymns, and spiritual songs, submitting to one another, admonishing one another, abounding in love for one another, encouraging one another, building one another up (this is not talking about ego building!), living in harmony with one another, outdoing in showing honor to one another, praying for one another, loving one another, seeking to do good to one another, stirring up one another to love good works, confessing our sins to one another, instructing one another, greeting one another, praying for one another, showing hospitality to one another, using our gifts to serve one another, clothing ourselves with humility toward one another, and having fellowship with one another. John's epistles talk much of 'loving one another'.
This seems to indicate that those who make up the body of Christ are supposed to be in relationship with each other. Maybe this is part of discipleship that seems to be missing today, in many, if not most, churches.
If people think of 'going to church' as attending a meeting once a week, without ever getting to know the other people that are part of that body, then the concept is wrong. The early disciples actually met every day, in houses. They seemed to be very committed to 'one another' as revealed by their actions as we see in the Scriptures.
The Bible also instructs us on things we should 'not' do to one another. For example, we are not to backbite one another. We are not to pass judgment on one another. We are not to compare ourselves to one another. Provoking one another is also not allowed as well as lying to one another. Some of these things should seem obvious to us, especially is we treat others the way we would like to be treated.
I know there are struggles people have with discipleship and trust issues. How do we know if we can trust anyone? We can trust the Lord at all times and He can guide us into the body of believers He wants us to be joined with. Over time, we can get to know people and we can learn who we can trust and how much we can entrust to them.
The Bible has a lot to say about love. Everything we do with one another has to be based upon love. If we are manipulative, or use people for our own ends, then we do not love. If we slander and gossip about people, we do not love. If we complain about people and do not try to work things out in our relationships with them, then we are not showing love and respect. We are not going to be best friends with everyone in the church, but we can serve those whom we get to know and who we become friends with.
You cannot get to know someone by looking at the back of their heads once a week. Getting to know people requires humility and intentionally reaching out to them. You will have no idea of what kinds of struggles the person sitting next to you is going through, unless you ask them questions that are deeper than 'How are you?' every week.
It takes time to get to know people and to trust them. People might put on a facade for a while, but over time, you will begin to see through it. Sometimes, people put on a mask because they are afraid of rejection. Sometimes, people put on a false front because they really do have evil intentions. Be patient with people and you will learn a lot about someone.
Relationships do not come overnight, nor do they come automatically. They take a lot of time to build them. Over time, trust develops. That doesn't mean we will never be hurt and betrayed, but the chances are better that hearts will be revealed as people reach out and try to draw someone out and get to know him or her.
I think we can look at 1 Corinthians 13 and see what love is all about. If we have any other motive than love, or if our love is mixed with other motives, then we need to let God change our hearts. We cannot build relationships without love in our hearts for one another. The Bible commands us to love God with all our hearts, souls, minds and strengths, and, to love our neighbor as ourselves. Our love for one another reveals whether we really love God or not. We can ask ourselves this question; Do we really want this other person to be successful, even though I will have to sacrifice some things in order for that to happen, or, do we want ourselves to be successful at the expense of our self love in place of love for them?