What does 2 Thessalonians 3:3 mean?

In this verse Paul and his coworkers express their confidence in the Lord. Because God is faithful, He could be trusted to strengthen the Thessalonians and protect them from Satan. Because God is faithful He will not allow evil men to gain a victory over believers.

The Bible assures us that God is completely trustworthy. Even when circumstances seem dim, He is faithful to sustain His people and bring good out of bad (Romans 8:28–29). Even when the prophet Jeremiah grieved over the fall of Jerusalem, he took courage in knowing that God is faithful. He wrote in Lamentations 3:21–23, "But this I call to mind, and therefore I have hope: The steadfast love of the LORD never ceases; his mercies never come to an end; they are new every morning; great is your faithfulness." The Lord is faithful to provide for our daily needs (Matthew 6:33; Philippians 4:19), and to provide the way of escape when we are tempted and tried (1 Corinthians 10:13).