Basic Spiritual Skills; 1 John 2:23
The basic claim that John is making related to salvation is that rejection of the unity of Father and Son is really implicit in the gospel. When we receive Jesus Christ as saviour, John is saying, that is the same as accepting the truth about God the Father. If God the Father is rejected then Jesus Christ is rejected, because in essence they are the same. Other passages that emphasise this are found in John 12:44, 45 NASB "And Jesus cried out and said, "He who believes in Me, does not believe in Me but in Him who sent Me. He who sees Me sees the One who sent Me." It is not just belief in Christ but belief in the fact that if He is the Son of God then there is some definition to the concept of God. Cf. John 14:10 NASB "Do you not believe that I am in the Father, and the Father is in Me? The words that I say to you I do not speak on My own initiative, but the Father abiding in Me does His works. [11] Believe Me that I am in the Father and the Father is in Me; otherwise believe because of the works themselves."
1 John 2:23 NASB "Whoever denies the Son does not have the Father; the one who confesses the Son has the Father also.