The promise of offspring is the promise of a new community through whom God is going to bless the world. This promise is fulfilled in a special way through Jesus Christ who is The Seed of Abraham, but also through those who are united to Him by faith.
Read Genesis 13:16
The promise of the land is very important in God's plan of salvation. It is fulfilled initially when Israel inherits the land of promise. It is further fulfilled in the salvation accomplished by Jesus Christ which is revealed as the inheritance of the spiritual seed of Abraham and finally fulfilled in the new heavens and the new earth.
Read Genesis 13:15