Whatever 2 Thess 3:3 means, it does NOT mean that Christ's followers will be protected from suffering and persecution - see appendix below. Indeed, in Acts 5:40, 41, the apostles regarded their Christian suffering as an honor:
At this, they yielded to Gamaliel. They called the apostles in and had
them flogged. Then they ordered them not to speak in the name of
Jesus, and released them. The apostles left the Sanhedrin, rejoicing
that they had been counted worthy of suffering disgrace for the Name.
Further, we read in Eph 6:10-16 that Christians need to wear spiritual armor to withstand the attacks of Satan. Thus, God does not prevent the Devil's attacks but does provide spiritual armor to enable us to withstand those attacks. Indeed, Eph 6:13-16 actually lists what these attacks will be:
- belt of truth to withstand false doctrine
- breastplate of righteousness to keep us from doing wrong
- shoes of the gospel of peace to spread the good news
- shield of faith to extinguish the darts (of doubt) from the Devil
- helmet of salvation to have the absolute assurance of eternal life
- sword of the Spirit to understand the inspired word of God.
This is the true way that "God is faithful and guards from the evil one" (2 Thess 3:3), not by removing suffering and persecution, but giving as the assurance of His presence with us, and protection from losing our trust in Him.
APPENDIX - Christians with Suffer and Experience Persecution
The NT makes it very clear that Christians are to expect suffering and persecution for their faith.
- John 15:20, 21 - Remember the word that I spoke to you: ‘No servant is greater than his master.’ If they persecuted Me, they will persecute you as well; if they kept My word, they will keep yours as well. But they will treat you like this because of My name, since they do not know the One who sent Me.
- John 16:33 - I have told you these things so that in Me you may have peace. In the world you will have tribulation. But take courage; I have overcome the world!”
- Heb 13:12, 13 - And so Jesus also suffered outside the city gate, to sanctify the people by His own blood. Therefore let us go to Him outside the camp, bearing the disgrace He bore.
- 1 Peter 2:21 - For to this you were called, because Christ also suffered for you, leaving you an example, that you should follow in His footsteps
See also 2 Cor 1:6, Col 1:24, 2 Thess 1:5, James 5:7-12, 1 Peter 4:14, 5:8, 9, etc.