Whoever believes that Jesus is the Christ is born of God… – 1 john 5:1

Mystery or no mystery, the new birth is yours if you are a believer. Have you never noticed that the greatest mysteries in the world reveal themselves by the simplest indications. The simplicity and apparent easiness of faith is no reason why I should not regard its existence as an infallible indication of the new birth within. How know we that the new-born child lives except by its cry? Yet a child’s cry-what a simple sound it is! how readily could it be imitated! a clever workman could with pipes and strings easily deceive us; yet was there never a child’s cry in the world but what it indicated the mysteries of breathing, heart-beating, blood-flowing, and all the other wonders which come with life itself. …Go into a telegraph office at any time, and you will see certain needles moving right and left with unceasing click. Electricity is a great mystery, and you cannot see or feel it; but the operator tells you that the electric current is moving along the wire. How does he know? “I know it by the needle.” How is that? I could move your needles easily. “Yes; but do not you see the needle has made two motions to the right, one to the left, and two to the right again? I am reading a message.” “But,” say you, “I can see nothing in it; I could imitate the clicking and moving very easily.” Yet he who is taught the art sees before him in those needles, not only electric action, but a deeper mystery still; he perceives that a mind is directing an invisible force, and speaking by means of it. Not to all, but to the initiated is it given to see the mystery hidden within the simplicity. The believer sees in the faith, which is simple as the movements of the needle, an indication that God is operating on the human mind, and the spiritual man discerns that there is an inner secret intimated thereby, which the carnal eye cannot decipher. To believe in Jesus is a better indicator of regeneration than anything else, and in no case did it ever mislead. Faith in the living God and His Son Jesus Christ is always the result of the new birth, and can never exist except in the regenerate. Whoever has faith is a saved man.~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0979.cfm