There are two ways "brother" is used in the Bible, ways that are still reflected in modern language. One denotes an actual blood relationship; the other is a more sweeping term of commonality, in such as in the phrase the "brotherhood of man." In general 'brother' in terms of the blood relationship refers to the unity that can exist between the desire to do good and the understanding of how to do good. This is true of Cain and Abel and several pairs of twins: Jacob and Esau, Judah's sons Zarah and Pharez, and Joseph's sons Ephraim and Manasseh; in each case one represents the desire for good and the other the understanding of truth.