God is the one who "said." Jesus uses the passive here to make it plain that it is not God or God's word that he disagrees with. Rather, he is saying that a divorce is just only if it occurs for the right reason. A divorce can be unjust even if the man obeys the command to give a written notice. (See: [[rc://en/ta/man/translate/figs-activepassive]])
The "I" is emphatic. This indicates that what Jesus says is equally important to the original commands from God. Try to translate this phrase in a way that shows that emphasis. See how you translated this in [Matthew 5:22](./21.md).
It is the man who divorces the woman improperly who "causes her to commit adultery." In many cultures it would be normal for her to remarry, but if the divorce is improper, such a remarriage is adultery.
This can be stated in active form. AT: "her after her husband has divorced her" or "the divorced woman" (See: [[rc://en/ta/man/translate/figs-activepassive]])