Albert Barnes Commentary Luke 12:35-36

"Let your loins be girded about, and your lamps burning; and be ye yourselves like unto men looking for their lord, when he shall return from the marriage feast; that, when he cometh and knocketh, they may straightway open unto him." — Luke 12:35-36 (ASV)

Let your loins, and so on. This alludes to the ancient manner of dress. They wore a long flowing robe as their outer garment. (See Barnes on Matthew 5:38-41).

When they labored, or walked, or ran, it was necessary to gird or tie this robe up with a sash or girdle about the body, so that it might not impede their progress. Therefore, to gird up the loins means to be ready, to be active, to be diligent. (Compare 2 Kings 4:29; 2 Kings 9:1; Jeremiah 1:17; Acts 12:8).

Your lights burning. This phrase expresses the same meaning: be ready at all times to leave the world and enter into rest when your Lord calls you. Let every obstacle be out of the way, let every earthly care be removed, and be prepared to follow him into his rest.

Servants were expected to be ready for the coming of their lord. If he came during the night, they were expected to keep their lights trimmed and burning. When their master was away attending a wedding, as they did not know the hour when he would return, they were to be continually ready.

So we, as we do not know the hour when God will call us, should always be ready to die. (Compare with Barnes on Matthew 25:1, and also Matthew 25:2-13).