Paul customarily brings his letters to a close with a section dealing with practical and personal matters and greetings
This second time he repeats the call twice, “Rejoice … again I will say rejoice!” and adds the word “always.” The joy of the Christian is not a passing quality. Rejoicing is not to be reserved for special times of worship or praise. It is to be uninterrupted and unbroken.
To begin by praising God for the fact that in this situation, as it is, he is so mightily God—such a beginning is the end of anxiety. To be anxious means that we ourselves suffer, ourselves groan, ourselves seek to see ahead. Thanksgiving means giving God the glory in everything, making room for him, casting our care on him, letting it be his care. The troubles that exercise us then cease to be hidden and bottled up. They are, so to speak, laid open to God, spread out before him.