In accordance with the laws and customs prevailing at the time of the Messiah, a man was regarded as the father of a child if he was married to child’s biological mother at the time she gave birth, regardless of who was responsible for its procreation, and also if he adopted the child. (And this law still applies today in Western countries.) If a man married a woman who had a child, as Joseph did, then in the original languages of the Gospel, he was usually described as the child’s “father” (for example, Greek pater). That’s true in English as well, however, the more precise description of this relationship in English is to say the child’s “stepfather.” In Arabic such a man can be described as “the husband of the child’s mother,” or as his “custodial parent” (وليّ أمره walī ’amrihi) or “the head of his household” (ربّ بيته rabbu baitihi) or “the head of his family” (ربّ أسرته rabbu ’usratihi) or just ربّه rabbuhu. So in the Injil Sharif, the Arabic word ab (اب) describes the man who functions in the role of the father in a family, even if he is not the biological father responsible for the procreation of the child.

This relational definition of a family differs greatly from the Arab family, which is defined strictly along biological relations. When the commonly used Arabic words أب ab and ابن ibn are used to describe relationships between members of a family, they have a narrow physical meaning; they mean biological father and biological son and not any other kind of father and son. They are not used for adoptive fathers and adopted sons, or step-fathers and step-sons, or foster fathers and foster sons, or for personal relations that are like those. As a result, they are not equivalent to the words commonly used for fathers and sons in Hebrew, Greek, and English, which are used for any relationship that is like that between a loving father and his son. Therefore these two words in the Gospel must be understood according to their meaning in the original languages and not according to their meaning in Arabic. 

Sadly, an ancient Arab sect, called “Collyridians,” interpreted أب and ابن in their usual Arabic sense of biological father and son and then assumed God had a wife named Mary and that they gave birth to the Messiah together, and that all three were gods. Such thinking is justly condemned because it reduces God to something like a man who reproduces other gods. This is contrary to the Scriptures, which teach that there is only one God and that he is far greater than humans and doesn't reproduce.