You'll both have well-formed opinions on the big issues in life -- religion, spirituality, morality, politics -- and you'll find that you disagree on many of these subjects. In a friendship, this will simply feel like an irritating divide. If you find yourselves pointing the finger at each other, you'll be wise to take it as a sign that you're reacting against the vulnerability that these fundamental differences will cause within you.
Compromise will be necessary in this case, but could be pretty difficult without good communication and mutual respect working in your favor. If you're able to accept the differences between you and not feel threatened by them, they shouldn't cause huge problems in your relationship.