‘Grace to you and peace from God our Father and the Lord Jesus Christ.’
Both grace and peace come from the same source, with the source being God the Father and the Lord Jesus Christ. This is a reminder to us of the equality between the Father and the Son. At the same time they remind us of two different relationships that Christians enjoy. First, they are children in the family of God and, second, they are servants in the household of Jesus.
In the ancient world the father of a family and the master of a household were responsible for meeting the needs of those who belonged to them. This is also the case with God the Father and with the Lord Jesus Christ. Of course, they also have the capability and the willingness to bless their people, which is a great encouragement to us.
Further, the fact that there is only one Father and one Lord Jesus Christ is an encouragement to unity of heart among believers. When we disagree, we do it with fellow sons of God and fellow servants of Christ, and that is not at all commendable unless there is a valid reason for the disagreement.
So Paul’s greeting is a prayer that the believers would be equipped for living the Christian life. I suspect that here he is speaking from experience: it was God’s grace that prepared him for his imprisonment in Rome, from where he wrote this letter, and it was God’s peace that enabled him to endure the imprisonment. And we can experience such grace and peace wherever we are today.