This is Paul's usual written greeting. But, unlike many social pleasantries (in Britain we ask, ‘How do you do?’ but nobody expects an honest answer!) it really means something. Paul knew that only the grace of God can bring peace. That is the gospel message for which he was in prison, that Christ Jesus came into the world to save sinners. It was also his personal testimony for he admitted he was the worst of sinners (1 Timothy 1:15). If Jesus could save Paul, He can save anybody! Nobody can have peace with God any other way (Romans 5:1).