This is a question we have been asked many times in our 23 years of ministry. We must answer it with the authority of God's Word. When Catholics repent and believe the Gospel of God, they are born again and the indwelling Holy Spirit will lead them out of spiritual darkness into the glorious light of Jesus Christ (Mark 1:15; Eph. 1:13-14). As they abide in God's Word, they will know the truth and the truth will set them free from religious bondage and deception (John 8:31-32). Then they will look for a church that worships God in Spirit and truth because that is the kind of worshippers God seeks (John 4:24). Anyone who says they have been born again, yet refuses to leave a false religion that deceives people with another gospel, must examine themselves to see if they have genuine saving faith (2 Cor. 13:5). Christians are called to walk according to the truth which means, as they become more and more passionate for the truth, they will turn away from any falsehood that stands opposed to God's Word.
One of Catholicism's false practices is described as a doctrine of demons in the Bible. Under the inspiration of the Holy Spirit, the Apostle Paul wrote that some will "depart from the faith by devoting themselves to deceitful spirits and teachings of demons through the insincerity of liars whose consciences have been seared who forbid people to marry" (1 Tim. 4:1-4). Catholicism is the only religion that names the name of Christ and forbids its clergy to marry, thus proving that some of its teachings are directly opposed to Scripture.
Another reason true converts must leave Catholicism is that it demands submission of every person's will and intellect to the bishops' teachings. Catholic bishops are said to be the only authentic instructors and teachers of the faith, and Catholics are bound to adhere to their teaching with a religious submission of the mind (Canon Law, 753).
A third reason to leave is that the Word of God condemns the Catholic clergy for preaching another gospel (Gal. 1:6-9). The Catholic plan of salvation nullifies God's saving grace by adding works, sacraments, purgatory and law-keeping to the Gospel. Not to be outdone, Catholic bishops responded by condemning born again Christians with over 100 anathemas from the Councils of Trent and Vatican II. Read more about anathemas.