What did God promise Christ would happen as a result of the cross and resurrection?

Les explains that God had promised Christ that His going to the Roman cross, dying, shedding His blood, and being raised from the dead would bring in this multitude of believers. Those believers were promised to Him from the very beginning. In the surrounding context, Les connects this to Galatians 4, where Isaac represents the children of promise, while Ishmael pictures the flesh and the persecution that continues between the believing element and unbelievers. The Scripture says to cast out the bondwoman and her son, which pictures the Law and legalism.