Mark 9:42
But whoever causes one of these little ones who believe in Me to stumble, it would be better for him if a millstone were hung around his neck, and he were thrown into the sea.
What does it mean to make them stumble?
One thing to immediately observe, is that the point is especially directed to those who take some planned conscious action against the innocent.
Its more than just leaving a barn door open, or losing your child in the crowded mall for a moment.
It refers to those who actually plot and carry out some action against the naive and defenceless, such as promoting smoking to young women and teenagers as "glamorous".
It might appear as 'innocent' as offering an underage person a beer, but the point is not to be deceived about God or the results of your actions:
God is not fooled nor mocked.
What an evil person sows (i.e., what he plans and carries out),
he will reap the consequences of. (i.e., severe punishment).
No one should actively or passively, knowingly contribute to another person's error, sin, or injury, especially for profit or selfish reasons.
God knows all things, including the hearts of humankind.
peace
Nazaroo