The most stumbling block to SALVATION among untold numbers of people is unbelief in the word of God:
“For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. For God sent not his Son into the world to condemn the world; but that the world through him might be saved. He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God” (John 3:16-18).
“But what saith it? The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach; That if thou shalt confess with thy mouth the Lord Jesus, and shalt [BELIEVE IN THINE HEART THAT GOD HATH RAISED HIM FROM THE DEAD, THOU SHALT BE SAVED]. For [WITH THE HEART MAN BELIEVETH UNTO RIGHTEOUSNESS[; and [WITH THE MOUTH CONFESSION IS MADE UNTO SALVATION]” (Romans 10:8-10).