12 The law is not based on faith; on the contrary, it says, “The person who does these things will live by them.”a

Read Galatians 3:12 Using Other Translations

And the law is not of faith: but, The man that doeth them shall live in them.
But the law is not of faith, rather "The one who does them shall live by them."
This way of faith is very different from the way of law, which says, “It is through obeying the law that a person has life.”