Note 9 at 1 Th. 2:18: This is an amazing passage of scripture. Many people don't think Satan has the power to hinder anything if an individual is in the center of God's will as Paul was. They mistakenly think that everything going smoothly is a token of God's direction (see note 3 at 1 Cor. 16:9, p. 969). Any problems we encounter must mean we missed God. That is not what Paul is describing here.

Satan has severe limitations and he cannot just devour everyone (1 Pet. 5:8), but there are certain things he can do to even those who are operating in the power of the Holy Spirit. The biggest area in which he can hinder us is when what we are believing for involves other people.

For instance, our financial prosperity involves others. People can't stop us from prospering, but they can certainly hinder us. And in the area of persecution, God will not just "wipe out" all those who oppose us so that we can preach the gospel without any hindrance. He loves even those who reject Him. God's mercy towards those who persecute us may cause us some hardships, but it allows the unbelievers the opportunity to receive salvation (see note 14 at 2 Cor. 12:7, p. 1041).

Paul made a similar statement to this one in Romans 15:22-23. In that passage, he explained that the hindrance to his traveling to Rome was that there were unreached people around him that he felt compelled to preach to before he could leave them. It is most probable that he is describing the same thing here. He wanted to return to Thessalonica but Satan was hindering the preaching of the gospel and so it was taking Paul longer than he anticipated to finish his work there.