John Gill Commentary Luke 17:1

"And he said unto his disciples, It is impossible but that occasions of stumbling should come; but woe unto him, through whom they come!" — Luke 17:1 (ASV)

Then said he to his disciples
In the Alexandrian copy, and in "three" of Beza's exemplars it is read, "his disciples"; and so read the Vulgate Latin, and all the Oriental versions; that is, Jesus said to his disciples what follows, as the Syriac and Persic versions express, and the latter reads, he said "again". About the time that he delivered the above parable concerning the rich man and Lazarus, he repeated to his disciples what he had before said to them on another occasion, (Matthew 18:7)

it is impossible but that offences will come ;
considering the decree of God, the malice of Satan, the wickedness of men, the corruption both of their principles and practices. The Ethiopic version renders it, "temptation will come"; that which will be trying to the faith of the saints, and a stumblingblock to weak minds, as reproach and persecution, errors, and heresies, and the evil lives of professors:

but woe [unto him] through whom they come ;
(See Gill on Matthew 18:7)