Without offering explanation, the Bible calls one person of the Trinity “Father” and another “Son,” and speaks of the Father “begetting” the Son (Psalm 2:7; Hebrews 1:5). Along with the Holy Spirit, the Father and the Son are eternal—having no beginning and no end.
In the Old Testament, God delivered many prophecies about the promised Messiah, his Son. Those prophecies included masculine pronouns. It comes as no surprise, then, that the angel Gabriel informed both Joseph (Matthew 1:21-23) and Mary (Luke 1:31) that the child born to Mary would be a son.
What a blessing it is to be able to call Jesus our Brother (Hebrews 2:11-12).