Praise be Jesus and Mary, now and forever. 
In today's first reading, taken from St. Paul's first letter to the Thessalonians, the Apostle is referencing the end times, the time of Christ's second coming, and he tells the faithful of Thessalonica that they are children of the light, 1 Thessalonians 5:5, that they need to be watchful and stay sober, so practicing temperance and self-control, verse 6. He adds that God has not destined us for wrath, but for salvation, verse 9. And then the first reading concludes with St. Paul saying, "Encourage one another and build one another up, just as you are doing," 1 Thessalonians 5:11.
In St. Paul's letters, he often offers profound theological reflections, a number of clear perennial moral instructions as well, and then he also adds practical concrete advice for living the Christian life. 1 Thessalonians 5:11 is both a profound theological reflection that's actually tied to practical concrete advice, advice that can easily get overlooked and neglected. "Encourage one another and build one another up," St. Paul says to the faithful. The word encourage there in the original Greek text is the word parakaleo. It means to encourage, exhort, even comfort. Our English word courage has the prefix en, which means to make or put in, and the word courage, which means courage of the heart. So to encourage someone is to help strengthen and put courage into their hearts. Again, the Greek word used by St. Paul is parakaleo.
When our Lord at the Last Supper speaks of the Holy Spirit, He calls the Holy Spirit the parakletos, which is translated as advocate or counselor, or comforter. Jesus says in John 14:26, "The counselor or the comforter, the Holy Spirit, whom the Father will send in my name, He will teach you all things." What does the Holy Spirit do? He sanctifies us, yes, but He also encourages us, exhorts us, comforts us in our difficulties. So when St. Paul tells us to encourage one another, he's actually saying be an extension of the Holy Spirit to others. It's actually a profound concept and an extraordinary reality when you think about it.
Apart from exhorting and comforting and encouraging, the Holy Spirit also confronts and convicts us when we've done something wrong. He enlightens us when we are in the dark or ignorant about something important. So yes, we are called to assist the Holy Spirit in our relations with fellow believers in all those dimensions, always encouraging them to do good, to do God's will, at times correcting them or admonishing them when they're in the wrong, which is a spiritual work of mercy, and other times offering them hope and comfort in their struggles.
And then when St. Paul tells us in 1 Thessalonians 5:11 to build one another up, the word for build there is a Greek word, oikodomeo. It's the same root word that we find in Matthew 16:18 when our Lord says, "You are Peter and upon this rock I will build, oikodomeo, I will build my Church." It's the same word St. Luke uses in Acts 9:31 when he says that the Church throughout all Judea and Galilee and Samaria had peace and was built up, again the root word there, oikodomeo. It's the same word that St. Matthew uses at the end of the Sermon on the Mount when he shares our Lord's words about being a wise man who built his house upon the rock, Matthew 7:24.
Which rock do we build our house, our spiritual lives upon? It's the rock of faith, of our belief in Christ, yes, but it's also the rock of Peter, the rock of the one whom Christ made as head of the Church. So when St. Paul tells us to build one another up, it's actually clearly a reference that's tied to the Church, tied to the building up of the body of Christ, as the Apostle speaks of in Ephesians 4:12. Encourage one another and build each other up. We are to assist the Holy Spirit who animates the Church, who gives different gifts to each one in the Church, as St. Paul says in Ephesians 4:11 and 12. We are to assist the Holy Spirit in building up and edifying the body of Christ.
The opposite of St. Paul's exhortation to encourage one another and build each other up would be to discourage one another and tear each other down. And both of those activities and realities, discouraging others, tearing them down, both of those activities and attitudes are not from the Holy Spirit. They are the work of the evil spirit. Those who discourage us spiritually include those who say that they are Catholic, but they discourage us from living a life of grace, most likely because their own lives and beliefs are contrary to the gospel. Those who tear us down include Catholics who encourage and cause us to sin, yes, because sin is what tears away at Christ's body. But it also includes those sins that a number of people don't consider sins, like tearing down the Church through disobedience, through dissent, through discord, through constant criticisms, through disparaging and disrespecting the hierarchy, through sowing seeds of doubt in the minds and the hearts of others regarding the magisterium. Those people also tear away at Christ's body, similar to how the flagellums tore away at Jesus' flesh during His scourging.
St. Paul in Ephesians 4:15 and 16 says, "Speaking the truth in love, we are to grow up in every way into Him who is the head, into Christ, from whom the whole body, joint and knit together by every joint with which it is supplied, when each part is working properly, makes bodily growth and upbuilds itself in love." The upbuilding of the Church in love. One of the things that both the extremes in the Church have in common, both the liberal progressive extreme and the traditionalist extreme, one thing that they have in common is that neither extreme really builds up the faithful in love, as St. Paul says we are supposed to do. It's one of the many flashing red lights that we need to be aware of and not ignore when dealing with such mindsets. And it's why we need to steer pretty clear from them, actually, frankly.
Those who have humble, teachable spirits don't remain on the extremes. Sooner or later, the Lord actually rescues them from those pitfalls, hopefully sooner rather than later. 
As much more we can say regarding encouraging others and building them up, but we'll stop here for today. We'll simply ask for the grace, ask Our Lady for the grace to assist rather than block the Holy Spirit in His work of sanctifying, building up, and expanding the body of Christ in the world. This world which truly needs to see unity and charity expressed in and through those of us who belong to Jesus. 
Praise be Jesus and Mary, now and forever.