Joh 17:24 "Father, I desire that they also whom You gave Me may be with Me where I am, that they may behold My glory which You have given Me;
for You loved Me before the foundation of the world.
How could God the Father love a Son who did not exist before the foundation of the world?
Jesus was the Son of God before his incarnation he is still the Son of God after his resurrection. Jesus has always been the Son of God.
“Son of God” refers to the humanity of Jesus. Clearly the humanity of Jesus is not eternal but was born in Bethlehem. One can speak of external existence in past, present, and future only with respect to God. Since “Son of God” refers to humanity or to deity as manifest in humanity, the idea of an eternal Son is incomprehensible. The Son of God had a beginning.
Paul wrote that this indeed came to pass in Christ: “For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ” (II Corinthians 4:6). In other words, the Son of God became the means by which the invisible, incomprehensible God revealed Himself to us.
It is apparent that many trinitarians interpret their doctrine to mean three personalities, three beings, three minds, three wills, or three bodies in the Godhead. They deny that by person they mean only manifestations, roles, or relationships with humanity. Instead, they defend an eternal threeness of essence while admitting it to be an incomprehensible mystery. They reduce the concept of God’s oneness to a unity of plural persons. By their definition, they convert monotheism into a form of polytheism, differing from pagan polytheism only in that there is perfect agreement and unity among the gods. Regardless of trinitarian denials, this leads to polytheism—tritheism to be exact—and not the monotheism taught by the Bible and upheld by Judaism.
The Sonship—or the role of the Son—began with the child conceived in the womb of Mary. The Scriptures make this perfectly clear. Galatians 4:4 says, “But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law.” The Son came in the fullness of time—not in eternity past. The Son was made of a woman—not begotten eternally. The Son was made under the law—not before the law. (See also Hebrews 7:28.) The term begotten refers to the conception of Jesus described in Matthew 1:18-20 and Luke 1:35. The Son of God was begotten when the Spirit of God miraculously caused conception to take place in the womb of Mary. This is evident from the very meaning of the word begotten and also from Luke 1:35, which explains that because the Holy Ghost would overshadow Mary, therefore her child would be the Son of God. We should notice the future tense in this verse: the child to be born “shall be called the Son of God.” (This is when He (the Word, became flesh) became the Son of God. He was not called the Son of God until His incarnation.