Matthew 19:10-12. Immediately following Jesus' teaching that a man who divorces his wife and marries another, or a man who marries a divorced woman, commits adultery, the disciples say to him "If such is the case... it is not expedient to marry." Jesus says to them "Not all men can receive this precept, but only those to whom it is given." He then goes on to say there are men who are born as eunuchs, there are others who are made eunuchs by other people, and there are others who have made themselves eunuchs for the sake of the kingdom of heaven. Jesus finishes by saying "Let he who is able to receive this, let him receive it."

Am I able to receive this word? I'm not sure, but let me think it through. Marriage is forever - there is no divorce in God's eyes. It is a covenant, like the one that he made with us. And marriage is good, or else the human race would not be able to "be fruitful and multiply" as God commanded us. But clearly not all people are called to marriage, and that is good, too. We all have to find our own purpose, our calling, in order to become what God wants us to be.

Jesus uses the example of eunuchs to drive his point home. Some are like that from birth - they simply cannot have sexual relations or procreate. So their calling is clearly to another vocation other than marriage. Some men are made eunuchs by others. This can be literal - it was not an uncommon practice to do this to slaves or criminals; but it also can be figurative - someone could have treated another so badly that he is psychologically unable to participate in a rightly ordered sexual relationship. All of these are tragic, but God never abandons us. These men, too, have a purpose and a calling that God will lead them to if they are open to him. Lastly, some men  become eunuchs willingly, giving up the possibility of a sexual relationship for the purpose of the kingdom. These men hear God's call and act on it. They are not meant for marriage in God's plan, they are discerning and holy enough to have realized that, and they devote themselves, instead, to God's work.

All of these examples are men who don't marry, not because it is not "expedient" as the apostles say, but because in God's plan they are not meant to. If they must give up this most basic human desire, then how can a man who does not have to give it up complain that he must, at least, limit himself to one woman?