It's hard to imagine that Paul the apostle feared anything, but he admits that he was afraid for the Corinthian believers- that they might be led astray by the devil's subtlety (2 Corinthians 11:3 RSV). I've found myself afraid of this very thing- that I could be and would be led astray by the enemy's influence.
None of us is immune. Proof of this is Paul's warning. We are also warned by Peter, too. He tells us that the devil is on the prowl and that we need to keep alert (1 Peter 5:8).
On the one hand, the devil is a disarmed and defeated foe (Colossians 2:15; Hebrews 2:14NASB). On the other hand, he exerts influence through trickery. He is committed to his objective to steal, kill and destroy (John 10:10). He is subtle (2 Corinthians 11:3), which means that his work is not obvious. He also seems tireless in his efforts to deceive us.
I have come to believe that there is no blessing that I aim to receive from God that will go uncontested by the devil. For this reason, we must expect that whenever we press in to God, we will experience push-back.
Soldiers don't expect to take ground without push-back, but when we Christians want to move forward, and experience resistance or retaliation, we tend to retreat. We need to learn to advance and to keep our eyes on Jesus while learning to resist the devil. We are promised that, if we resist, he will flee from us (James 4:7).
Have you asked God for the fortitude to fight? Are you asking Him to help you to avoid falling prey to the enemy's schemes?