What is the most important thing about Christianity to you?
Love. I cannot say this or stress this enough. God is love. We were made by God and for God. Therefore we were made by love and for love. It is the very core of everything. It is interwoven and imbedded into every infinitesimal detail of who we are.
The two most important commandments involve love. Love the Lord your God with EVERYTHING you are and love your neighbor as yourself.
The most important thing about Christianity (and life, for that matter) is love.