Note 14 at 1 Th. 5:16: As mentioned in note 2 at Philippians 3:1, page 1166, the word "joy" is a noun describing a person, place, or thing. The word "rejoice" is a verb describing the action of a person, place, or thing. So, the command to "Rejoice evermore" is a command to act.

Most people view emotions, such as joy, as reactions to what is happening to us. But godly emotions are based on what Christ has already done for us regardless of what is happening in our physical world. Otherwise, Paul would be unreasonable to command us to always rejoice.

Bad things happen even to good people. If emotions were just our physiological responses to problems or the lack thereof, then there is no way we could keep this command. But emotions are an action based on our choice. If we choose to focus on what Christ has done for us, then we can rejoice in spite of our environment. This is not a suggestion, it's a command.

Note 15 at 1 Th. 5:16: The word "evermore" literally means "at all times" (Strong). No one wants to be miserable. People don't wake up in the morning and pray for depression. But very few people take any responsibility for the way they feel. They think feelings are just automatic responses to what happens to us. That is not so. We can choose how we feel.

Our feelings follow our thoughts. If we think on negative things, whether real or imagined, we will have negative emotions. If we think on the wonderful things God has done for us, we will have positive emotions, regardless of what our physical circumstances are (Rom. 8:6). Rejoicing at all times has nothing to do with what is currently happening to us but it has everything to do with focusing on what has already happened to us and what has been promised to us in Christ.