Matthew 8:22

θάψαι τοὺς ἑαυτῶν νεκρούς. The exact force of this is not quite clear. The word ‘dead’ is used first in a figurative, secondly, in a literal sense, as in John 11:25-26. In a figurative sense by the ‘dead’ are intended those who are outside the kingdom, who are dead to the true life. Perhaps a brother or brothers of the disciple had rejected Christ, ‘let them bury their father.’

St Luke, after ‘let the dead bury their dead,’ adds, ‘but go thou and preach the kingdom of God.’
Perhaps no incident marks more decisively the height of self-abandonment required by Jesus of His followers. In this instance the disciple is called upon to renounce for Christ’s sake the last and most sacred of filial duties. The unswerving devotion to Christ is illustrated in the parallel passage (Luke 9:62) by ‘the man who puts his hand to the plough.’