Paul was imprisoned in the Roman barracks in Jerusalem.  He was being protected from the Jewish mob and religious leaders by the Roman commander.

A conspiracy to kill Paul had been formed by over forty Jewish men.  Paul’s nephew, his sister’s son, found out about it and came to Paul and told him during the evening hours.  (Acts 23:16)

(NASB) Acts 23:17-22 “Paul called one of the centurions to him and said, ‘Lead this young man to the commander, for he has something to report to him.’
18 So he took him and led him to the commander and said, ‘Paul the prisoner called me to him and asked me to lead this young man to you since he has something to tell you.’
19 The commander took him by the hand and stepping aside, began to inquire of him privately, ‘What is it that you have to report to me?’
20 And he said, ‘The Jews have agreed to ask you to bring Paul down tomorrow to the Council, as though they were going to inquire somewhat more thoroughly about him.
21 ‘So do not listen to them, for more than forty of them are lying in wait for him who have bound themselves under a curse not to eat or drink until they slay him; and now they are ready and waiting for the promise from you.’
22 So the commander let the young man go, instructing him, ‘Tell no one that you have notified me of these things.’”

How did the Lord protect Paul?
1-His nephew heard the details of the Jewish plot to kill Paul.
2-Paul alerted one of his Roman jailers, a centurion, asking him to take his nephew to the commander.
3-The centurion carried out Paul’s request immediately.
4-The commander listened intently to the report of the young man and did not doubt the information.
5-The commander then acted decisively and quickly.
6-The commander warned Paul’s nephew to tell no one he had talked with him.

Had Paul done anything to protect himself physically?  No.

Paul was a man of prayer.  Prayer was probably given before his nephew came with the news of the conspiracy.

Prayer is imperative, important and brings about improbable results from a human perspective.

God used various people to accomplish His purpose for Paul.  Even the unnamed person who told the young man of the plot against Paul.

All of us need God’s protection in some way… how will you now pray for your circumstances?