Third Watch

Luke 12:37-39 (New International Version)It will be good for those servants whose master finds them watching when he comes. I tell you the truth, he will dress himself to serve, will have them recline at the table and will come and wait on them. It will be good for those servants whose master finds them ready, even if he comes in the second or third watch of the night. But understand this: If the owner of the house had known at what hour the thief was coming, he would not have let his house be broken into.

A commentary:
Now Jesus makes a comparison. Like servants who wait for their master to return from a wedding celebration, disciples should be ready for their Lord to appear anytime at the door. Wedding feasts could last for as long as a week, so the time of someone's return was not always predictable. Servants had to be ready to serve whenever the master broke loose from the party to return home. Disciples should live in the same expectation.
Jesus offers a beatitude for those who heed his advice (v. 37); NIV introduces it with it will be good. The NRSV more closely follows the Greek: "Blessed are those slaves whom the master finds alert when he comes." The beatitude has an interesting twist: when the master returns, he will serve the servants who are faithful. Jesus has always placed a high premium on service, and here he shows that he will honor faithfulness with service. It is not at all common for masters to serve slaves, but God's grace shows the extent of God's love. The chief steward leads the stewards in service. He will share the meal at the table of fellowship and serve the food. The imagery suggests the blessing of being totally accepted by Jesus.
But Jesus does not tell his disciples when the master will return. The allusion to the second or third watch gives a general time frame, though the exact time is uncertain because it is not clear if Luke intends a Jewish three-watch or a Roman four-watch schedule. Either way the time frame is "deep night," somewhere between midnight (Roman time) and 2:00 a.m. (Jewish time). Luke uses the Roman schedule elsewhere (Acts 12:4), but a Jewish setting might suggest the other possibility. Either way the point is clear: the disciples must be ready because the return may be at any moment, even deep in the night when one normally would not be prepared. Constant vigilance is expected.
Jesus extends the call to readiness by comparing his return to a thief's robbing a house at night. Just as a man would never leave his house exposed if he knew a robber was going to try to enter it, so the disciple should be ready for the Son of Man's return. For just as we do not know when a thief may come, so we must be ready at all times. The Son of Man will come at an unexpected hour. There is spiritual exposure in lack of preparedness. The thief image suggests that the risks of unpreparedness are great.

Romans 13:10-12 (New International Version)
Love does no harm to its neighbor. Therefore love is the fulfillment of the law. And do this, understanding the present time. The hour has come for you to wake up from your slumber, because our salvation is nearer now than when we first believed. The night is nearly over; the day is almost here. So let us put aside the deeds of darkness and put on the armor of light.