Albert Barnes on Matthew 19:12

Jesus proceeds to state that there were some who were able to receive that saying, and to remain in an married state. Some were so born; some made such by the cruelty of men; and some who voluntarily abstained from marriage for the kingdom of heaven's sake--that is, that they might devote themselves entirely to the proper business of religion. Perhaps he refers here to the ESSENES, a sect of the Jews Mt 3:7 who held that marriage was unsuitable to their condition, who had no children of their own, but perpetuated their sect by adopting the poor children of others. Eunuchs were employed chiefly in attending on the females, or in the harem. They rose often to distinction, and hold important offices in the state. Hence the word sometimes denotes such an officer of state, Acts 8:27.

(h) "kingdom of heaven's sake" 1Cor 7:32