God will internally motivate man to obey him
Ancient Israel was not given the ability to obey their Creator both in the law's letter of the law and spirit (Romans 8:3). God promises with his new agreement that, through the power and might of his Holy Spirit, he will personally write his laws and ways on man's mind.
'I will give My laws into their minds, and I will inscribe them upon their hearts; and I will be their God, and they will be My people.' (Hebrews 8:10) 1. Consequently, there is now no condemnation to those who are in Christ Jesus, who are not walking according to the flesh, but according to the Spirit; (Romans 8:1)
King David, who had God's Holy Spirit in him, describes what will happen after our Father's laws are written in us.
How I love to do your will, my God! (Psalm 40:8)
ALL our sins will be forgiven
The second reason why what Jesus Christ offered in the New Testament is greater than anything before it is because it promises ALL sins will be forgiven. In fact, the tremendous promise God makes is that our sins, once he forgives them, will NEVER, EVER be recalled or remembered by him!
12. For I will be merciful toward their unrighteousness, and their sins and their lawlessness I will not remember EVER AGAIN. (Hebrews 8:12)
It is only through the sacrifice and death of Jesus Christ, the Savior of mankind, that such an incredible and awesome forgiveness can be extended to man (Matthew 26:27-28).
God's children will receive an eternal inheritance
The third and final reason (promise) the new proposed covenant is far greater than anything else is that those who love and obey God will receive an inheritance only HE can give.
15. And for this reason He is the Mediator of the New Covenant: in order that through His death . . . those who have been called might receive the promise of the eternal inheritance. (Hebrews 9:15)
Soon offered to all Israel
Although God's new proposal to live forever is being offered to only a relative few now, it soon will be proposed to ALL Israel - and indeed to all man who ever lived (Ezekiel 37, Jeremiah 31, Hebrews 8, etc.). Although only partially fulfilled during his first coming to earth, the primary mission of Jesus' SECOND coming will be to encourage man to accept God's will for them.
And the Lord, whom you seek, will suddenly come to His temple, even the MESSENGER OF THE COVENANT, in whom you delight. (Malachi 3:1)
Under the rule of Jesus the world will come to know, respect, and keep God's law.
God made humans for a particular reason and purpose. Out of his perfect love he wants to share ALL he has, forever, with as many beings as possible. First, however, he must develope in us holy righteous character, the same character he and Jesus have had eternally, so that we can fully appreciate all that he generously wants to give.
Ultimately EVERY human will be given a FULL chance to hear and understand the gospel, and then decide whether they wish to live God's way eternally or not. It is through his incredibly amazing new covenant that God fulfills his will to have countless billions of spiritual children just like him.