When Paul wrote these words, we know that they come from his own personal experience:
“Therefore, since we have been made right in God’s sight
by faith, we have peace with God
because of what Jesus Christ our Lord has done for us.” – Romans 5:1
It seems that one of the things that alludes many faith seekers is a genuine Peace with God. We try our best to please God with all kinds of religious practices and rituals, but these don't always give us peace.
I guess that Paul could speak from both perspectives - from being zealous and obeying all religious laws, to really knowing authentic PEACE with God.
"So, since we have come to be considered righteous by God because of our trust, let us continue to have shalom with God through our Lord, Yeshua the Messiah." - Complete Jewish Bible