Isaiah 58 reminds us that the house of Jacob was very religious. Unfortunately, they were religious in the same way the surrounding nations were. The house of Jacob used Spiritual disciplines like fasting to try to get God to help them get what they wanted and not because they were genuinely repentant. God wanted them to fast from their wickedness, but they fasted from food. They fasted from food, but they did not give bread to the hungry. Their self-denial was selfish. Sometimes mixed into our motives for doing the religious thing is an effort to manipulate God to do whatever it is that we want. The Christian walk is a life of self-denial, there is nothing wrong then with self-denial, the problem is the heart. Are we denying ourselves because it really would help others or are we doing it so that we can keep on doing our own thing? But thanks be to God that Jesus purifies all of the good things we do from mixed motives.