‘And Jesus said to them, “The sons of this world marry, and are given in marriage, but those who are accounted worthy to attain to that world, and the resurrection from the dead, neither marry, nor are given in marriage, for neither can they die any more. For they are equal to the angels, and are sons of God, being sons of the resurrection.” '
Jesus' reply, indicating a detailed knowledge of the afterlife which demonstrated His heavenly origin, declared that the question was based on the failure of the questioners to appreciate the truth about the afterlife. For in the afterlife there is no such thing as marriage and reproduction. Those raised from the dead at the resurrection become similar to the angels, with spiritual bodies (1 Corinthians 15:44), and become ‘sons of God' (an Old Testament title used of angels - Genesis 6:2; Genesis 6:4; Job 1:6 to Job 2:7; Job 38:7) indicating their then enjoying a wholly spiritual nature and body, similar to that of God and the angels. They cannot die any more, and thus reproduction is unnecessary. They are ‘sons of the resurrection', that is products of the results of God's resurrection power resulting in eternal life.
‘Those who are accounted worthy to attain to that world, and the resurrection from the dead.' Jesus' emphasises here that not all will experience resurrection to life, and enjoy the life of the age to come. Only those who will be considered fit and suitable because God counts them as worthy (e.g. Genesis 15:6) will attain to that world. (Thus not all of the seven brothers, for example, would necessarily experience it). And they will thus have become immortal, and will never again experience death, will not marry or have children, but will enjoy a similar life of immortality to that of angels enjoying their ecstasy, not in sex, but in enjoying the presence of God.
(Thus those who teach a millennial kingdom on earth have the problem of having a mixture of spiritual beings who cannot bear children, mixing with physical beings who can have children. This is not the impression given by taking all that is said in the Old Testament in its overly-literal meaning e.g. Isaiah 65:17-25).