Why did God do the work of the cross and send the Holy Spirit?
God did the work of the cross, the power of His resurrection, and the coming of the Holy Spirit to fulfill the New Covenant He will make with the house of Israel. Believers in the Age of Grace enjoy those blessings as members of the Body of Christ, but not in a covenant relationship.
Les explains that Jeremiah 31:31 promises a New Covenant God will make with the house of Israel and with the house of Judah. Many theologians claim believers in the Age of Grace are under that New Covenant, but Les says plain English shows the covenant is made with Israel, not with the Body of Christ. Therefore, God did the work of the cross, the power of His resurrection, and the coming of the Holy Spirit to fulfill this covenant with Israel. Age of Grace believers enjoy the benefits of those blessings, but they are not in a covenant relationship; they are members of the Body of Christ, with Christ as the Head.
Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah: