One of those is Lent. As I celebrate it now with my current church, I celebrate it as a time of sacrifice and renewal. I sacrifice something that in my "normal" life is consistent with what I do or who I am. Usually this is a dietary item, but I have also tried the technological realm as well (I gave up facebook, blogging, and email for 40 days one year). The sacrifice helps remind me that God is bigger than my wants or my needs. That I should rely on God for all that I am and want to be. It also reminds me that the world cannot promise me anything, only God's promises are eternal.
Renewal comes in different ways. Sometimes people choose to not only sacrifice something from their daily routine, but also pick up a new habit that is a spiritual exercise. Maybe they choose to say Psalm 23 every day or say the Lord's Prayer. They might also choose to use the money they save from buying a coke every day to put towards mission efforts. Either way they are renewing their commitment through a physical activity. Renewal also comes through humility, prayer, and meditation. We can use the 40 days to really ponder how God wants to use us for His kingdom purposes.
The season of Lent is a journey of sacrifice and renewal that when practiced grows us to be more like Christ and a stronger force for the kingdom. Giving up things is hard to do. What will you give up these next 40 days?