Woe unto the world because of offences - That is, offences will be the cause of woe or of suffering. Offences, here, mean things that will produce sin: that will cause us to sin, or temptations to induce others to sin. See the notes at Matthew 5:29.
It must needs be ... - That is, such is the depravity of man that there will be always some who are attempting to make others sin; some people of wickedness endeavoring to lead Christians astray, and rejoicing when they have succeeded in causing them to fall. Such, also, is the strength of our native corruption and the force of passion, that our besetting sins will lead us astray.
Woe to that man by whom the offence cometh - He who leads others into sin is awfully guilty - no man can be more guilty. No wickedness can be more deeply seated in the heart than that which attempts to mar the peace, defile the purity, and destroy the souls of others; and yet in all ages there have been multitudes who, by persecution, threats, arts, allurements, and persuasion, have endeavored to seduce Christians from the faith and to lead them into sin.