Some, we understand, who voluntarily approached the waters of holy baptism, do not entirely cast off the old man that they may more perfectly put on the new one, because, retaining remnants of the former rite, they obscure by such a mixture the beauty of the Christian religion. But since it is written: "Accursed is the man that goeth on the two ways" (Ecclesiastes 2:14), and "a garment that is woven together of woolen and linen" (Deuteronomy 22:2) ought not to be put on, we decree that such persons be in every way restrained by the prelates from the observance of the former rite, that, having given themselves of their own free will to the Christian religion, salutary coercive action may preserve them in its observance, since not to know the way of the Lord is a lesser evil than to retrace one's steps after it is known.
Essentially, if a Jew has converted, it is important that bishops and others prevent them from being exposed to Jewish rites lest they turn away from Christianity. If not being a Christian was bad, then being Christian and deliberately abandoning it was even worse.
This was not the same as being a non-Christian in the first place, since "ignorance of the law was an excuse." If you had not been made Christian through lack of exposure (or coercion), you were simply non-Christian and living in error. But to deliberately turn away from a Christian life was a subversion of the social order according to the Justinian Code.
This was worse than being a heretic. A heretic was a Christian who erroneously believed certain points that were counter to the accepted tenets. A heretic was still a Christian, and persuasion (or coercion) could bring the "lost sheep" more fully into the fold.
An unrepentant apostate could be excommunicated, a way of saying "You want to quit? Well, then you're fired!"
Augustine of Hippo claimed that the "gift of perseverance" in Christian faith was a gift from God, and that an individual cannot know if God has granted them this gift. Without it, it was possible that a Christian might leave the faith.
How did Jews look at those of their faith who converted? Let's talk about that tomorrow.