"keep on the alert"
Jesus said “keep on the alert” four times (Mk. 13:33, 34, 35, 37).
The reason is because we don’t know when the appointed time will come (v. 33).
Since we don’t know when the Lord is coming,
We must be on the alert (v. 35).
Jesus said “If he comes suddenly,
Do not let him find you sleeping” (v. 36).