Here this does not mean the Old Testament or the Ten Commandments but rather the instructions that Paul gives in [1 Timothy 1:3](../01/03.md) and [1 Timothy 1:4](../01/04.md).
Here "pure" means the person does not have hidden motives to do wrong. Here "heart" refers to a person's mind and thoughts. Alternate translation: "from a mind that is honest" (See: [[rc://en/ta/man/translate/figs-metonymy]])