Causing others to sin
Luke 17:1-3 is a warning about serious sin (skandalon) that causes another to stumble (cf. Lev. 19:14; Judges 8:27; 1 Sam. 25:31; Psa. 119:165). Woe to him that through false teaching - by word or deed - that causes another to fall. Hughes says:
In this fallen world all these stumbling blocks will come. But, says Jesus, woe to that person through whom they come. We must interpret this woe very carefully. Jesus did not say the woe upon the offender is that he will have a millstone tied around his neck and be tossed into the sea. Being cast into the sea is the way to escape the woe. The woe is far worse.
It would be better to die (even a horrible death) than to cause a little one to stumble and ultimately incur the woe of which Jesus warns. Better for the disciple or leader or pastor to die than to teach errant doctrine. Better to die than to have a lifestyle that trips others. Better to die than to have attitudes that drive others away from Christ.
I must confess that I do not understand what woe could await a true believer who has scandalized others away from Jesus Christ that could make a horrible physical death preferable, but I believe what the Savior is saying. Maybe the woe is an official dressing-down at the Judgment Seat of Christ, with shipwrecked "little ones" there as accusers. Such a one is "saved, but only as one escaping through the flames" (1 Corinthians 3:15). Whatever Jesus meant, death now is better than the woe. And thus Jesus' warning, "So watch yourselves" (Luke 17:3a) must be taken to heart. Watch your teaching. Watch your lifestyle. Watch your attitudes.