The reason for Paul’s failure to return to Thessalonica was that Satan hindered us.
Travel was an essential feature of Paul’s entire ministry, and he often speaks about the way in which his travel plans were either brought to fruition or hindered. Most often, the fulfillment or frustration of his plans is associated with the sovereignty and providence of God (see, e.g. Romans 1:10–13; Romans 15:22–23; 1 Corinthians 16:5–7; Acts 16:6–10). It is noteworthy, then, that Paul identifies Satan as the supernatural agency preventing his return to Thessalonica.
Paul identifies Satan as the one who prevented him from returning to Thessalonica because he recognizes that the new believers are involved in a spiritual battle (see Ephesians 6:10–18; 1 Peter 5:8). Satan is their adversary, who seeks to draw them away from Christ (1 Thessalonians 3:5). He will do anything he can to undermine their faith, and one of his tactics is to keep Paul from visiting the Thessalonians to encourage and strengthen them spiritually.
Though Satan (a powerful, evil spiritual being) was the cause of Paul’s inability to return to Thessalonica, he must have worked through Paul’s practical circumstances to accomplish his goal. Scholars have made various suggestions regarding the actual means that Satan used: perhaps there was renewed Jewish opposition to the gospel in Thessalonica; perhaps Jason and the others would have lost the security they had been forced to pay if Paul had returned (Acts 17:9); perhaps Paul became sick. The truth is that we do not know what the actual circumstances were, but it is worth noting that Satan does work through everyday circumstances in his efforts to oppose the work of Christ.1,2
18 because we wanted to come to you I, Paul, again and again but Satan hindered us.