In what form did sin exist in the centuries after the Fall? Gen. 4:8; Gen. 6:5, 17. Why were Sodom and Gomorrah destroyed? Gen. 18:24,32; Gen 19:24,25.
The world before the Flood had every opportunity to know God's law. That world was destroyed because people chose to disobey and live in sin. Likewise, Sodom and Gomorrah were destroyed because the people rejected the moral stipulations of the divine law. To assert that early humans were so primitive that they could not know the moral imperatives that exist in modem societies is to accuse God of injustice in destroying the antediluvian world and the cities of Sodom and Gomorrah. When Jesus compared the world immediately before His second coming to the world before the Flood, he offered no excuse for early humans on the grounds of their ignorance of His moral law. (See Matt. 24:37-39.)
How did the Lord preserve knowledge of His standard of righteousness prior to Sinai? Gen. 7:1; Gen. 26:5.
The great men and women of faith who lived before the giving of the written law at Sinai were sinners in need of the Saviour. Noah and Abraham bad lapses from faith. God focused on their spiritual victories attained by complete dependence upon Him. Not only was Noah a preacher of righteousness (2 Peter 2:5), he practiced what he preached by allowing the righteousness of God to be demonstrated in his life. God could identify him as "righteous" (Gen. 7:1), because, by faith, he lived by the righteous principles of the divine law. Although Abraham is presented in Scripture as the great example of life by faith, he had serious lapses from obedience by faith in God (Gen. 16:1-4; Gen. 20:2; Gal. 4:21-31). Even so, God praised and blessed Abraham's consistent faith and obedience to His law (Gen. 15:6; 26:5).
"Some few in every generation from Adam resisted his [Satan's] every artifice and stood forth as noble representatives of what it was in the power of man to do and to be--Christ working with human efforts, helping man in overcoming the power of Satan. Enoch and Elijah are the correct representatives of what the race might be through faith in Jesus Christ if they chose to be."--Ellen G. White, Review and Herald, March 3, 1874.
What answer can you give to those today who assert that faith excludes the necessity of obedience?