John Gill Commentary Luke 12:40

"Be ye also ready: for in an hour that ye think not the Son of man cometh." — Luke 12:40 (ASV)

Be you therefore ready also
Not habitually, but actually, in the exercise of grace, and the discharge of duty, with loins girt, and lights burning. This may be understood either of a readiness to meet the Lord in the way of his judgments, and particularly the destruction of Jerusalem, which was to be in a few years; or of a preparation for death, and the last judgment, which lies in the righteousness of Christ imputed, and his grace imparted: and to have a comfortable view of the one, and a gracious experience of the other, as they will engage to the performance of good works, to which such are ready; so they make meet for the coming of Christ, be it in what way, and whensoever it will: and the rather, a concern should be had for such a preparation, because of the following reason,

for the son of man comes at an hour when you think not ;
in either of the above ways; (See Gill on Matthew 24:44).