The existence of only one God can be known with certainty through reason alone, therefore it is rational. That Jesus Christ is the same Person as this one God can be known without faith. He fulfilled all of the prophecies in the Old Testament, said He was God, and performed miracles that only God could perform, There were many moral miracles as well. That the gentiles were converted to Catholicism from paganism is beyond reason as they were living a life of pretty much doing whatever felt good to them and then became Catholic and we all know that there is a lot of rules that go along with that! They were pretty much signing their death sentence at the time and many were martyred. Furthermore, we can know that Catholicism is that same religion due to even more miracles throughout the ages, such as the Miracle of the Sun that took place only 100 years ago and which was witnessed by over 70,000 people, many of whom came to mock the prediction that the Fatima children made 3 months ahead.