3:11 So it is clear that no one can be made right with God by trying to keep the law. For the Scriptures say, “It is through faith that a righteous person has life.” 3:12 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.”
The New Living Translation is not poetry, but I had a hard time understanding the other translations.
The World English Bible says the quote in 3:11 is to Habakkuk 2:4:
Look at the proud! They trust in themselves, and their lives are crooked. But the righteous will live by their faithfulness to God.
(OPB: NLT)
… and that in 3:12 to Leviticus 18:5:
If you obey my decrees and my regulations, you will find life through them. I am the LORD.
(OPB: NLT)
Paul is pretty explicit that the time of the Mosaic law has been and gone, but I’m more interested in the positive side of these verses, and the Habakkuk. I understand the message to be that faith is paramount. Following rules in and of itself cannot bring you to God. Only faith in God can lift you up.
To an unknown God 
Bill (cycleguy) said
YOu got it Ivan! Rules and regulations will not bring us to God. That is why Paul also says that law cannot save us. (Gal.2:15-16, which you have already read). It is only faith in Christ that can.