Others may have thought Jesus was John the Baptist risen from the dead, but as can be seen by looking at Matthew's Gospel and especially Mark's, Herod was convinced of this personally. This shows Herod's own conviction of the sin John had rebuked, his guilt and torment over his even greater sin of beheading John, and his fear of John and the God he represented.  As seen in Mark 6:20, Herod once listened to John gladly.  It is certain that John was preaching his favorite message of, "Repent ye: for the kingdom of heaven is at hand." For Herod to hear him gladly, he must have been under deep conviction from God.

Herod feared his wife and the opinion of others more than he feared God.  Herod was not as Festus, who told Paul he was mad for speaking of the resurrection from the dead.  Herod knew the truth personally, was exceedingly sorry, and yet chose death, both John the Baptist's and his own spiritual death.  Apparently Herod lacked peace after his fatal choice.

According to the world's mentality, peace is the absence of problems.  God's peace is not dependent on circumstances.  It is dependent only on God Himself who is the same yesterday, today, and forever (Hebrews 13:8).  A Christian can have great peace even in the midst of terrible problems because his faith is in God. "Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee" (Isaiah 26:3).