“But because he did not have the wherewithal to pay, his lord commanded him to be sold, and his wife, and children, and all that he had, and payment to be made.”
And when he could not pay his debt his lord commanded him to be sold, along with his wife and children and all his possessions so that something of what he owed might be paid. This was a normal procedure with a largish debt, or a huge one like this. They then joined the ranks of bondmen and bondwomen, and slaves. This was always the fate of the bankrupts of the day. But none of them would fetch even a talent in the markets of that day, and most a good deal less. The thought was not of repayment of the debt so much as punishment for letting the situation arise. It is a reminder that if we give all that we have, and our own lives also, it could not even put a scratch on the debt that we owe to God.
We should note that even this act is merciful. Once sold off nothing more will be done to him. He is not suffering the worst possible scenario, that of being tortured so as to ensure that he is not hiding his assets and then in order to squeeze out of his family whatever they could pay (compare Matthew 18:34).