On the left at the bottom we see St. Paul's execution ordered by Nero (see detail).  In the center foreground he is led to his execution, which we see on the right at the bottom (see detail). 

As he awaits the sword, Paul has tied over his eyes the kerchief he borrowed from a disciple named Plautilla.  In the center background (see detail) we see her receiving it again from the new saint, who is "more clear and more shining than the sun, and hath brought again my keverchief all bloody which he hath delivered me." (The Golden Legend's life of St. Paul recounts this episode.)

In the upper right we see a lion devouring a doe or calf (see detail).  This appears to refer to a sentence in the Golden Legend rehearsing one of the persecutions that St. Paul suffered: "In Ephesus he was delivered to wild beasts."  The Legend's source is probably St. Paul's more conditional statement in 1 Cor 15:32, "If (according to man) I fought with beasts at Ephesus, what doth it profit me, if the dead rise not again?"  He also uses the metaphor of wild beasts in 2 Tim 4:17, "But the Lord stood by me, and strengthened me, that by me the preaching may be accomplished, and that all the Gentiles may hear: and I was delivered out of the mouth of the lion."

More of St. Paul