If you're more comfortable talking about things in terms of Reformed theology instead of relationships and you really want to go down that rat-hole, the "works of the Law" Paul specifically mentions in his letters (see Romans 13-15 and Galatians 2, 5, and 6) were basically Jewish holiness distinctives: Circumcision, kosher diet, Shabbat observance, and the Jewish festivals. These are what separated God's people from the Nations. Paul nowhere disagrees with Torah regarding adultery, murder, lying, stealing, giving to the poor, welcoming strangers.... or trusting God.
"Justification" means being declared or judged "right with God" or righteous. So, Paul's conclusion is being right with God is by trust, independent of the Jewish holiness distinctives.