In an ideal world, there would be nothing but peace and harmony between the children of God. But we live in a fallen world, and that impacts believers as well. That means problems between believers happens. Martin Luther, commenting on Galatians 5:16, has some words of advice for when that happens,
Therefore the apostle has established this as a rule for the saints: that they should be servants of one another through love, that they should bear one another’s weaknesses and burdens (6:2), and that they should forgive one another’s trespasses (Matt. 6:12-15). Without such epieikeia (Greek word) it is impossible for peace and concord to exist among Christians. It is unavoidable that you are offended frequently and that you offend in turn. You see much in me that offends you; and I, in turn, see much in you that I do not like. If one does not yield to the other through love on matters like this, there will be no end to the argument, discord, rivalry, and hostility. Therefore Paul wants us to walk by the Spirit, so that we do not gratify the desires of the flesh. It is as though he were saying: “Even though you are aroused to anger or envy against an offending brother or against someone who does something unkind to you, still resist and repress these feelings through the Spirit. Bear with his weakness, and love him, in accordance with the command: ‘You shall love your neighbor as yourself.’ For your brother does not stop being your neighbor simply because he lapses or because he offends you, but that is the very time when he needs your love for him the most. The commandment ‘You shall love your neighbor’ makes the same requirement, namely, that you not submit to your flesh – which hates, bites, and devours when it is offended—but that you fight back at it by the Spirit and that through the Spirit you continue in your love for your neighbor, although you may find nothing in him that deserves your love.”
Luther, Martin Luther’s Works, v. 27, Lectures on Galatians 66-67