The "Only" is the key to understanding the mystery of God and of the Father and of Christ. This mystery of "One" is revealed.
Is JESUS the first begotten God or not? JESUS as the first begotten is revealed as God Himself. God said to the Son, "Thy throne, O God," explained as One Spirit. Flesh and blood cannot inherit the kingdom of God. Is JESUS the man, God; or, does the glorified man, JESUS Christ, just have the Spirit of God in Him?