Why couldn't the law save us, and what did the cross do instead?
The law could not save us, but the work of the cross has redeemed us. As soon as we are redeemed, God places us by the right of adoption into a place of full maturity in the body of Christ, giving full responsibility positionally while we grow in grace and knowledge.
The teaching explains that Scripture presents two concepts. A new believer enters the body of Christ as a babe in Christ—whether six or sixty—and desires the sincere milk of the Word, the simpler things. As the believer grows through the Christian experience, he or she becomes ready for the strong meat of the Word. Positionally, however, the moment a person is saved, God places him or her in the place of full responsibility, like the tutored son or little lad who was taught, encouraged, and reprimanded by his tutor, until the day he was presented as a full partner with the father. Ephesians 1:5 speaks of having been predestinated unto the adoption, and this adoption does not mean being legally transformed from one family to another. Thus, the law could not save; the cross redeemed, and redemption brings adoption into full maturity in the body of Christ.