By Does your love for the church testify to the world, or
does your love for the world deny the saints?
1 John is the most direct in its explanation of the love Christians have for one another. In summary form, the teaching of 1 John sounds like this:
1st, you cannot claim to know the Gospel if you do not love those in the church,
2nd, since God is love, you are not of God if you do not love the saints,
3rd, if you are truly saved, then you will love other Christians—it is a simple cause-and-effect,
4th, if there is no obvious expression of your love for the church, then there is no obvious proof of your love for God, and
5th, to claim to be loved by God is to pledge yourself to obey God and to love Christians.
By this all people will know that you are my disciples, if you have love for one another.
John 13:35