A.T. Robertson Commentary Luke 12:37

"Blessed are those servants, whom the lord when he cometh shall find watching: verily I say unto you, that he shall gird himself, and make them sit down to meat, and shall come and serve them." — Luke 12:37 (ASV)

He shall gird himself (περιζωσετα). Direct future middle. Jesus did this (John 13:4), not out of gratitude, but to give the apostles an object lesson in humility. See the usual course in Lu 17:7-10 with also the direct middle (verse 8) of περισωννυω.