The book doesn't say to believe in "Christ alone" to be saved. It says to believe that he is lord and son of GOD and has been raised from the dead, and be born again. "Christ alone" is an evangelical/reformed invention.
Christ alone is the anointing Holy Spirit of God. We are anointed from heaven through Him alone. It is his way of laying his hands as His will upon us. He is not served by human hands.
He warns us of those that he calls the anti-christs that insist on the works of the flesh, as the anointing of human will . As
it, His faith teaches us we abide in Him. Not the will of man represented by the laying on of hands, the ceremonial law (not needed)
These things have I written unto you
concerning them "that seduce you". But the
anointing which ye have received of him abideth in you,
and ye n
eed not that any man teach you: but as the same
anointing teacheth you of all things, and is truth, and is no lie, and even as
it hath taught you,
ye shall abide in him.1Jo 2:26
Christ alone is the term he has designed as the one who does all the work . It reforms the church not the other way around.