During the time that Jesus walked the earth many mistook the words the passion of Jesus to mean, the love of Jesus Christ. It goes way deeper then that. It is described in the books of Mark, Matthew and John, along with the book of Acts as the suffering of the messiah. Through out these books the story of the true messiah comes to light. The messiah is turned away and unbelieved by his people (the Jews). He (Jesus) is constantly challenged by his own crew (the disciples). He has to always show examples of who he is (miracles). He tells of his death and what happens after his death (the crucifixion and resurrection). Many of the day thought he was crazy, that no way was the true messiah be made to suffer all that he did. That is not what they believed according to God's law. Jesus always, always stated who he was and what his purpose on earth was. Until his dying breath he stayed on course. So when one is passionate about something, there is a fierce burning drive inside. There is a underlying agreement that suffering is part of this because you would do anything for your belief. That is passion.
Acts 1:3 To whom also he shewed himself alive after his passion by many
infallible proofs, being seen of them forty days, and speaking of the
things pertaining to the kingdom of God.