How was Abraham righteous without obeying the Ten Commandments?

Many insist that we still "need" to keep the Ten Commandments because it is by law we know right from wrong, and that we can only be righteous by continuing to obey the law even while living in grace.

If so, many great men in the Bible had no chance to be righteous because the Ten Commandments were given after their time.

Enoch wasn't righteous, Noah wasn't righteous, Abraham wasn't righteous, Isaac wasn't righteous, Jacob wasn't righteous, and even Joseph couldn't have been righteous. They didn't have the Ten Commandments to follow!

But is that so? Certainly not! God counted them righteous by their faith and in His grace (Hebrews 11). Were they perfect? No. But did they have a heart to obey God? Yes! Their true obedience is not in any set of laws, but by only their faith in the goodness of God. 

And in such intimate connection they knew in their hearts and minds right from wrong even without the written law. (Genesis 39:9)

They did not obey because they felt they had to (law), but because their faith brought them to an union with God (spirit).

This is the essence of grace, pure grace. And it was only possible because they didn't have "the law" on their minds. Today, God also wants us not to be under the bondage of law in order to live fully in grace.

Before the law the Israelite complained in the wilderness but still were blessed, and not one died. After the Ten Commandments were given each time they murmured they died. 

This is the fate of man's bondage to law. If we are under law we suffer the consequences of not keeping it; and in breaking just one we break them all, the Bible tells us.

But by the grace of Christ we no longer are under the curse of the law (Galatians 3:10,13) -- yet it is only up to us to believe or not. 

If we have a mind for righteousness by both grace and law we become double-minded and confused as to how we stand with God, and always have a fearful expectation of judgment. Otherwise we become like the pharisees being so self-righteous and full of pride in their own works of "obedience."

No. The law was given to show man up as to how inadequate he is to achieve holiness on his own (by obeying law). Once we come to that realization (repentance) law has already done its job, for it brought us back to the grace of God.

We then must return fully to only faith in grace and God's goodness evidenced by the cross that we are made eternally righteous in the blood of Christ. And for our faith to grow the law (believing we must obey or else) must be lifted, never again to judge and condemn a believer that he is not good enough.

The world will be judged, not for sins but the singular sin of their unbelief (John 16:8 & 9). If we still hold on to law as having anything to do with our righteous standing with God we still do not believe that grace has fully restored us back to the glory of His righteousness.

Therefore we have forfeited the gift of righteousness by such lack of faith..., even if we keep perfectly the law.