Without seeking to solve all the exegetical and theological problems of this passage, it is sufficient here to point out that prayer for physical health is in order. The conditions under which missionaries labor differ depending on the countries where they serve. In many countries of the world sanitation is very poor. Food and water may be contaminated. Proper medical facilities can be in short supply or even non-existent.
Constant prayer is necessary for the health of the missionary family.
Genuine love is the lubricant that makes for good relationships. Missionaries must have happy relationships with people if they are to be effective for God. This is not always easy just as it is not for us who are here at home. It is important that our requests to God include this important matter. Missionaries need to get along well with fellow missionaries.