“I can do all things through Christ which strengthened me” Philippians 4:13.
Peace is not a commodity that we can buy and sell, peace is a person. So what Paul is saying is that he has learned to be content because he knows in whom he has entrusted his life. Many different circumstances have proven that Jesus Christ has always been sufficient. When we develop a solid relationship with God then peace can rule in our hearts. So forming a habit of spending time with God will help us find that close relationship and in that we will know Him, trust Him, and peace is the result.