Augustine says that Peter's denial was not one of unbelief but of fear. No surprise there. Peter still believed that Jesus was who He said He was but Peter was so afraid of the consequences of that belief that he lied and denied Christ.
Our actions are based only partly on our belief. Our actions are generally based on
trust or fear. Fear about what might happen or trust about what might happen. Not trust that God will make everything go well but
trust that God can make wine out of water, redemption out of a cross, something good out of suffering if need be. We must not be afraid to suffer. We must believe that God is a God who does not end all suffering but does use suffering.