1 Thessalonians 3:12

"May the Lord make your love increase and overflow for each other and for everyone else, just as ours does for you." NIV translation

Paul's wish for the Thessalonian believers is quite simple and that is an increase in love. God is love and that is how His people will be made known. Paul wants them to draw closer to God so that they will love people more and that love will lead more people to accept Jesus.

1 Thessalonians 3:13

"May he strengthen your hearts so that you will be blameless and holy in the presence of our God and Father when our Lord Jesus comes with all his holy ones." NIV translation

Paul's final prayer for the believers here is for God to give them strength to follow Jesus. It is not easy to be holy but that is our calling and we cannot do so on our own. Paul knew that the ability comes from God through the working of the Holy Spirit.