It is a big subject so let us start with one factor. Son of God.
The title "Son of God" is not to be confused with "the only Son of God".
441 In the Old Testament, "son of God" is a title given to the angels, the Chosen People, the children of Israel, and their kings. It signifies an adoptive sonship that establishes a relationship of particular intimacy between God and his creature. When the promised Messiah-King is called "son of God", it does not necessarily imply that he was more than human, according to the literal meaning of these texts. Those who called Jesus "son of God", as the Messiah of Israel, perhaps meant nothing more than this. (CCC)
This was then extended to "the only Son of God" - the pre-existent Word (Logos).
John 10
31 Again his Jewish opponents picked up stones to stone him,
32 but Jesus said to them, “I have shown you many good works from the Father. For which of these do you stone me?”
33 “We are not stoning you for any good work,” they replied, “but for blasphemy, because you, a mere man, claim to be God.”
34 Jesus answered them, “Is it not written in your Law, ‘I have said you are “gods” ’ ?
35 If he called them ‘gods,’ to whom the word of God came—and Scripture cannot be set aside—
36 what about the one whom the Father set apart as his very own and sent into the world? Why then do you accuse me of blasphemy because I said, ‘I am God’s Son’?
John 3:16
For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
John 1
1 In the beginning was the Word, and the Word was with God, and the Word was God.
2 He was in the beginning with God.
3 All things were made through him, and without him was not any thing made that was made.
Matthew 11:27
All things have been handed over to me by my Father, and no one knows the Son except the Father, and no one knows the Father except the Son and anyone to whom the Son chooses to reveal him.
240 Jesus revealed that God is Father in an unheard-of sense: he is Father not only in being Creator; he is eternally Father by his relationship to his only Son who, reciprocally, is Son only in relation to his Father... (CCC)