This is a good question. Some things about this have not been revealed to us, but there are a few things that are clear. First it is important to understand that the Law of Moses was not given to all men (Neh. 9:9-14). God told the Israelites that the Mosaic covenant was not made with their forefathers, but with those descendants of Jacob who were at Sinai (Deut. 5:1-5). In doing this the Israelites were honored above all other people as God’s “special people” (Deut. 26:18). Why did God give a Law to Israel and not to the whole world? Paul taught that Mosaic Law was “added because of transgression” (Gal. 3:19). He explained that it was given so that “sin might appear sin” (Rom. 7:13). He described it as a “tutor” to bring men to Christ (Gal. 3:24). So, the Law came because of sins that were being committed, to show more clearly sin’s sinfulness, and to point the way to Christ.
We should note, if Mosaic Law was added “because of transgression” it tells us something important about God’s relationship with non-Israelites before and after the Mosaic Law. We know that “where there is no law, there is no transgression” (Rom. 4:15). Yet, even before the Law of Moses there were things that were considered sins (e.g. Gen. 4:7; 18:20; 20:9; 39:9). The clear inference of this fact is that there was some law that defined sin. This was not a revealed written law, as the Mosaic Law was for Israel. It appears to have been spoken directly to the patriarchs. Nevertheless, it held mankind accountable.
Some have tried to contend that the only way that one could be saved before Christ was to convert to Judaism. However, this doesn’t seem to be what is recorded in Scripture. Jonah was sent to preach repentance to the pagan Assyrian city of Nineveh (Jonah 1:1-2). He did so, and they repented (Jonah 3:5-10), but their repentance did not involve becoming Jewish proselytes. The book of Obadiah was a rebuke against the pagan Edomites. The book of Nahum was another rebuke to Nineveh. Hiram, the king of Tyre (2 Chron. 2:12), the queen of Sheba (1 Kings 10:9), and king Darius of the Medes (Dan. 6:26) were all Gentiles that praised God but did not follow Mosaic Law. Nebuchadnezzar was punished by God, repented, and was restored to his senses and praised God, but he did not follow Mosaic Law (Dan. 4:28-37).
So clearly, God’s covenant with Israel did not mean that God didn’t care about the Gentiles. Paul declared that God did not leave Himself “without witness” but provided for the Gentiles (Acts 14:17). Romans chapter one gives us a summary of the world’s rejection of God that tells us some things about His relationship to the Gentiles. It declares:
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, because what may be known of God is manifest in them, for God has shown it to them. For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse, because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened. Professing to be wise, they became fools, and changed the glory of the incorruptible God into an image made like corruptible man--and birds and four-footed animals and creeping things. Therefore God also gave them up to uncleanness, in the lusts of their hearts, to dishonor their bodies among themselves, who exchanged the truth of God for the lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen (Rom. 1:18-25, NKJV).
We can see from this that at first all mankind “knew God” (1:21) because God had “shown” them “what may be known of God” (1:19). This was true in different ways. The witness of God in nature left mankind without excuse (1:20). But it is also clear that God had “shown” them other things by some type of revelation, in that they “exchanged the truth of God for a lie” (1:25). After this summary of Gentile disobedience, in the next chapter Paul explores Jewish hypocrisy. In doing so he declares:
…For when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them) in the day when God will judge the secrets of men by Jesus Christ, according to my gospel (Rom 2:14-16, NKJV).
Even though Paul speaks of judgment according to the gospel and writes this after the Law of Christ was already in force, it is clear that he is talking about their standing before the coming of Christ. When they did what was right (according to the law of God that governed them before Christ) they were a “law unto themselves.”
All of this indicates that from Adam to Christ Gentiles were held accountable to what we could call the Patriarchal Law. We don’t know much about it, but we can know a few things about it. It taught one-man for one-woman for life” (Matt. 19:8). It prohibited adultery (Gen. 39:9) and premarital sex (Gen. 34:7). It prohibited murder (Gen. 9:6). It prohibited idolatry (Rom. 1:23), and involved some laws of sacrifice (Heb. 11:4; cf. Rom. 10:17)
Christ’s death and establishment of the New Covenant changed this diversity between Jew and Gentile. Paul explained this to the Ephesians. He wrote:
Therefore remember that you, once Gentiles in the flesh--who are called Uncircumcision by what is called the Circumcision made in the flesh by hands--that at that time you were without Christ, being aliens from the commonwealth of Israel and strangers from the covenants of promise, having no hope and without God in the world. But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity (Eph. 2:11-16, NKJV).
We note that in Christ the “wall of separation” is now broken down having “made both one” (2:14). Now God commands “all men everywhere to repent” (Acts 17:30). Now, all people will be judged by Christ’s words (John 12:47-48). Now, those who do not obey the gospel will be lost (2 Thess. 1:8-9). In the age to come, any who receive forgiveness of sins, who were obedient to the Law to which they were amenable, whether Jew or Gentile, from our age or from the Patriarchal, or Mosaic age will be saved by the blood of Christ (Heb. 9:15) as it is applied to their lives under the Law they were expected to follow.
Kyle Pope, May 2011