why was the pope so powerful?
The Pope, in and of himself, has very little to no "power". At one time, he was the secular ruler of a pretty big territory in Italy, and, at that time, had secular power. However, he is only the Vicar of Our Blessed Lord, and, as such, all the real power belongs to God, and the Pope is just the humble servant of the servants of God. In terms of everyday life, he wielded more influence back in the early centuries when, as a whole, people were more religious and faithful, and realized what was important in life. As the faith has grown weak, his influence has gotten to be less.