The only sure path to union with God is the love of Jesus Christ. All subordinate ways and means-- fasting and discipline-- must be subsumed by and ordered toward charity, without which it is empty (see 1 Corinthians 13 on this very point!).
The heretics of every age have always had a false rigor about them. In the 1200s St. Dominic came upon some Albigensian heretics who were far more rigorous than the Catholics themselves were. The problem was that their theology was shot through with a hatred for creation which viewed material things as evil. They abstained not because they loved but because they hated. The Church does not direct us to abstain from material things because they are evil. Rather, they are good, and the Church exhorts us to abstain for the sake of something better.
The gnostic and dualist heretics abstained from food and sexual intercourse because they thought it would trap souls in matter-- and they wrongly thought that ‘salvation’ was the freeing of souls from matter. The Christian knows that food and sexual intercourse are very good things, but abstains from them, perhaps, to show that God has created us as more than just beings who can attain to material goods. We are rational, spiritual beings within whom God Himself may tabernacle.
Thus Jesus says that, if you wish to be perfect, sell what you have and come follow me (Matthew 19:21). Jesus says that when the Bridegroom is gone, then his disciples will fast (Matthew 9:15). Jesus says that there are those who give us marriage for the sake of the kingdom of heaven-- and that those who can do this, ought to do this! (Matthew 19:12). Jesus gives a place to voluntary poverty for the gospel, fasting, and indeed celibacy. These are all central to the ‘life of perfection’-- the religious life, called the life of perfection because it is objectively ordered toward Christian holiness.
But the Christian gives these up as lesser goods, not as evils. The heretics give these up but they have only “an appearance of wisdom in promoting rigor of devotion” because they do not arise from the virtue of charity and slander the one true Creator God by counting His own creation as evil. But the Christian who takes up these practices will, like Jesus Christ, walk far on the path of charity.
-Rob