April 5: Belief, covenant, and ritual

Genesis 15

Abram is still bopping around without any kids, and in this passage he asks God what's up with that promise. This passage includes a description of an ancient covenant ritual. The Bible says in verse 6 that Abram believed, and in verse 9 Abram begins the ritual, at God's direction. If Abram believed, why did God have him perform this ritual?