I’d say that I am Catholic because:
— The Church has an unbroken history from the time of Christ.
— The form of the New Testament was determined by this Church.
— Christ said, ‘You are Peter, and on this rock I will build my Church’ and only the Catholic Church claims succession from St Peter.
— Christ said that the gates of Hell would not prevail against the Church. Meaning the Church would never die out… and it hasn’t over a period of 2000 years.
— Christ said to Peter, ‘I will give you the keys to the Kingdom of Heaven, whatever you bind on earth shall be considered bound in heaven, and whatever you loose on earth shall be considered loosed in heaven’. This has allowed the Church to continue to develop over the ages making what it is today.
…and on a more personal note:
— I’m Catholic because God led me to be Catholic.