Paul’s desire for all believers was that they were completely sanctified, that is holy, set apart for God. This is not about sinlessness, which no one will achieve in this life. We must set apart every aspect of our lives for God including relationships, school or work, hobbies, food, entertainment, sexuality—everything. Our lives should be wholly lived for God and in accordance with His will. Paul clarifies this by saying that our whole spirit and soul and body should be kept blameless. Again, he’s not talking about sinlessness but obedience and being above reproach. Every part of us must be lived for God. It’s no use trying to dedicate your spirit and soul to God but then sinning in the body. This is not something we can do by trying harder. God must do the work in us. God calls us to live this way and, if we submit to Him, He will surely do it. Can your life be described as blameless? What specifically do you need to change for that to be true of you? Is there an area where you’re trying too hard and you need to let God do the changing?

Paul asks the church for prayer reminding us that we must pray for our leaders.
He sends greetings to all the brothers (and sisters) with a holy kiss. This was a conventional greeting of the time. Today it might be a hug or a handshake (or an elbow bump).
These letters Paul wrote were intended for the whole church and to be passed on to other churches, even though they dealt with specifics in one church, the lessons are applicable to all of us.