His fight was not against “flesh and blood.”
While St. Paul traveled from town to town preaching the Gospel of Jesus Christ, he had an adversary who constantly attacked him. He describes the relentless battle in his Second Letter to the Corinthians.
And to keep me from being too elated by the abundance of revelations, a thorn was given me in the flesh, a messenger of Satan, to harass me, to keep me from being too elated. Three times I besought the Lord about this, that it should leave me; but he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” (2 Corinthians 12:7-9)
In other translations the term “messenger” is replaced by “angel.” Scholars continue to debate the exact meaning of Paul’s phrase, with some claiming that the “messenger” was an actual person who gave Paul struggles. Others believe that Paul had a physical “thorn” that gave his body great pain. Another possibility is that Paul was speaking about a spiritual enemy, a demon (“angel of Satan”) who continually attacked Paul.
This last option is something that would be consistent with Paul’s letters, as he frequently relates the reality of spiritual warfare. His most famous passage on this topic is from his letter to the Ephesians.
Put on the whole armor of God, that you may be able to stand against the wiles of the devil. For we are not contending against flesh and blood, but against the principalities, against the powers, against the world rulers of this present darkness, against the spiritual hosts of wickedness in the heavenly places. (Ephesians 6:10-12)
If Paul did battle with an “angel of Satan,” it reminds us that sometimes God allows such an attack to strengthen and humble us. As St. Paul wrote in his First Letter to the Corinthians, “God is faithful, and he will not let you be tempted beyond your strength, but with the temptation will also provide the way of escape, that you may be able to endure it” (1 Corinthians 10:13).
There are no other references to this “angel of Satan” in Paul’s letters, but it is clear that this was a constant battle that God allowed. Paul may have struggled much of his life battling this demon, but the good news is that the demon did not have the last say. As he wrote in his Second Letter to Timothy, “I have fought the good fight, I have finished the race, I have kept the faith. Henceforth there is laid up for me the crown of righteousness, which the Lord, the righteous judge, will award to me on that Day, and not only to me but also to all who have loved his appearing” (2 Timothy 4:8).