The believer must support his brother. The nouns used in the previous phrase are

The answer is: The believer, his brother.

A believer should always show his support for his brother or sister. This means that they have to be there for them no matter the situation. This includes providing emotional comfort, advice and physical assistance when necessary. They must also be willing to forgive any mistakes made by their sibling in order to maintain a healthy relationship between them. What is important is that the believer treats his brother with respect and understanding, even if they do not agree with them. By doing this, they will show true loyalty and love for their brother and build a strong friendship between them.