Peter knew that Jesus is the Christ, the Son of the living God.
“Simon Peter answered, “You are the Messiah, the Son of the living God.” Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven.”Matthew 16:17
“Every good gift and every perfect gift is from above, coming down from the Father of lights, with whom there is no variation or shadow due to change.” James 1:17
We should discern what comes from God the Father because of how good and perfect it is. Jesus discerned the revelation by which Peter knew Him because Jesus discerned its goodness and perfection. You know it was a good and perfect revelation, coming as it did to Peter from the Father. Not some mediocre revelation that would need to be revised later to fix the imperfections and defects. Not a shadow of truth that would change.
