Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ (Romans 5:1)
Beginning in Romans 5, Paul will begin to explain some of the blessings of righteousness by faith through Jesus Christ.
The first one he mentions is peace with God.
Justified by Faith.
In the context of what Paul has been saying:
We are not justified by the Law of Moses.
We are not justified by our own works of merit.
We are justified by faith through the sacrifice of Jesus Christ.
Those who are justified by faith enjoy a new relationship with God - they are blessed with a new standing with God.
The justified have peace with God.
Peace with God.
The peace Christians have with God is indicative of the relationship with presently have with Him (see Romans 5:10). We are no longer enemies of God and alienated from Him, but now are in a relationship based on His love and forgiveness. This peace comes through Jesus Christ, and not through the Law. More specifically, it comes through Jesus Christ our Lord. - Pollard, Truth for Today Commentary, 167
No matter what they face in their lives, the justified can rest well at night knowing they have peace with God.
After describing such a dark, bleak picture of where sin will take humanity in the first three chapters of Romans - what a wonderful thought it is to know that we can have peace with God!
Peace with God is offered to people who had jumped “headlong” into sin - even the kinds of sins Paul had discussed in the second half of Romans 1. They, too, could have “peace with God.”
Peace with God is only “through our Lord Jesus Christ.”
The MEANS of obtaining that peace is presented here to serve as a reminder of that doctrine developed through the last chapter. It is not THROUGH law, or THROUGH works of merit, but THROUGH Jesus Christ. - Wacaster, Studies in Romans, 180