These have indeed an appearance of wisdom in promoting self-made religion and asceticism and severity to the body, but they are of no value in stopping the indulgence of the flesh.
This verse describes three ineffective means of stopping my sin. At the top of the list is self-made religion. Picking and choosing my own moral code and custom built belief system is just a bad idea according to God. But it is the prevailing philosophy of religion in Western Culture. When Christian faith is restricted to the realm of "personal, private belief", with no voice in the public square or exchange of ideas, not held as an objectively sourced platform with truth claims, then all religion becomes self-made. "That's your interpretation..." is the mantra of many confronted with the exclusive claims of Jesus from the New Testament. But it is not up to me to determine right and wrong. My sin will always blur lines.
Asceticism is another failed way to fight sin that seems so promising. Withdrawing from all contact with anyone or anything might stop outward struggles to a degree. There are still monasteries to hide in. But this does not deal with the heart. There have been many bitter, hatefilled, sin struggling ascetics.
Severity to the body, extreme self-discipline, might also have a short-term effect on my outward sin,. But my problem is deeper... it is in my soul. I must change from the inside out. That is why trusting Jesus and receiving His forgiveness is the only way to deal with what is wrong with me.