Is anything mastering you?

Paul states in 1 Corinthians 6:12 "All things are lawful for me, but not all things are profitable. All things are lawful for me, but I will not be mastered by anything." NASB

In reading A Hunger for God I had to ask my self what is mastering me? A self examination should be done often and I have forced myself to ask some tough questions about my walk with Christ. What is really important to me in this life? Am I allowing desires for other things to choke the word and keep me from growing closer to Him?  Please share your thoughts on what masters you.

When should you fast?

Piper's book "A Hunger For God" explores the Christian Fast and explains fasting from a historical prospective. He states that Fasting  is a universal religious practice and is often use as a political weapon and for dietary reasons. But why must Christians fast?
Christ, being first in all things, fasted for 40 days in the wilderness before He began His ministry. Christ prepared himself for the work ahead. So when should we fast?