Albert Barnes on Luke 12:35-36

Let your loins, &c. This alludes to the ancient manner of dress. They wore a long flowing robe as their outer garment. Mt 5:38-41. When they laboured, or walked, or ran, it was necessary to gird or tie this up by a sash or girdle about the body, that it might not impede their progress. Hence, to gird up the loins means to be ready, to be active, to be diligent. Comp. 2Kgs 4:29; 9:1; Jer 1:17; Acts 12:8.

Your lights burning. This expresses the same meaning. Be ready at all times to leave the world and enter into rest, when your Lord shall call 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 in the night, they were expected to keep their lights trimmed and burning. When their master was away in attendance on a wedding, as they knew not the hour when he would return, they were to be continually ready. So we, as we know not the hour when God shall call us, should be always ready to die. Comp. Mt 25:1 and Mt 25:2-13.

(f) "Let your loins" Eph 6:14, 1Pet 1:13 (g) "your lights burning" Mt 25:1,13