“And Jesus saith unto him, Verily I say unto thee, That this day, even in this night, before the cock crow twice, thou shalt deny me thrice.”
Mark 14:30 — Greek Interlinear
Church Fathers on Mark 14:30
As they returned thanks, before they drank, so they return thanks after drinking; wherefore it is said, 'And when they had sung an hymn, they went out into the mount of Olives,' to teach us to return thanks both before and after our food.
For by a hymn he means the praise of the Lord, as is said in the Psalms [Ps 22, 26, 29], 'The poor shall eat and be satisfied; they that seek after the Lord shall praise Him.' And again, 'All such as be fat upon earth have eaten and worshipped.'
That hymn in the Gospel of John may also be meant, which the Lord sang, returning thanks to the Father, in which also He prayed, raising His eyes to Heaven, for Himself and His disciples, and those who were to believe, through their word.