We can't comprehend

it's hard

Then said he (Jesus) unto the disciples, It is impossible but that offenses will come: but woe unto him through whom they come! It were better for him that a milstone were hanged about his neck, and cast into the sea than that he should offend one of these little ones.

Considering the general corruption of human nature, the snares of the world, and the temptations of Satan, it cannot be but that one way or other offenses will be given or taken: stumbling blocks will be laid in the way of such as are traveling to the heavenly Jerusalem, and many will stumble at them, and fall over them; will be hindered in the way, or turned out of it; for many professing my religion will act in a manner very unsuitable to it, unworthy of themselves, and disgraceful to the Holy name they bear. BUT woe unto him through whom they come - Let me warn you, therefore, as you love your own souls, to guard against the guilt and danger of being stumbling blocks in the way of others. I assure you that such a one, (It were better for him) especially he that by an immoral life proves a reproach and scandal to my cause, had better die by the hand of violence, and suffer the most shocking execution, than that should offend, or cause to stumble and fall, one of these little ones, that is one weak believer, or any other of my despised and persecuted followers.

~Benson Commentary~