"Not all men can receive this saying" (19:11). Which saying does Jesus mean, and who is 19:12 about?

Here is exactly what the verses say. Jesus had said, "whoever divorces his wife, except for sexual immorality, and marries another, commits adultery" (19:9). His disciples said, "If this is the case of the man with his wife, it is not expedient to marry." (19:10). "But he said to them, “Not all men can receive this saying, but those to whom it is given." (19:11). Then he spoke of eunuchs "who were born that way from their mother’s womb", eunuchs "who were made eunuchs by men", and eunuchs "who made themselves eunuchs for the Kingdom of Heaven’s sake", and ended, "He who is able to receive it, let him receive it." (19:12). The verses don't name the saying beyond this saying, and Jesus doesn't say more in this chapter about who is meant in 19:12. Christians read these verses in more than one way. These notes quote them exactly, don't choose a reading, and apply them to no one's marriage or singleness.