The answer to this question depends on whether it is in reference to people before the birth of Jesus or after.

People before the birth of Jesus

Before the birth of Jesus, the gospel did not exist. God made His unilateral unconditional covenant when Abraham was in existence and much later would partially fulfill it with the birth of His only Son Jesus.

From the very beginning with Creation, human beings knew of and had a relationship with God. After the Fall, when sin came between human beings and God (Gen 3:1-19; Rom 5:12), the Bible records Cain and Abel making sacrifices.

The significance of the sacrifices wasn't understood until God makes the Mosaic Covenant. The sacrifices were for the atonement of personal sins (Lev 1:4) which required that the grain offering (i.e. Cain's) must be paired with the animal offering (i.e. Abel's) (Num 15:1-4).

Thus, while the sacrificial system of covering sin was not explained in the earliest biblical accounts, God instituted a procedure to expiate sin so that man could maintain a relationship with God. Despite the covenant relationship, the apostle Paul explains how human beings fell away from God:

For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, because that which is known about God is evident within them; for God made it evident to them. For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. Professing to be wise, they became fools and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures. (Rom 1:18-23)

Beginning with Adam, hiding from God after sin was introduced (Gen 3:8), human beings have forsaken God; God was not the one who walked away from their relationship.

When God "saw that the wickedness of man was great on the earth, and that every intent of the thoughts of his heart was only evil continually (Gen 6:5)," He judges mankind's sins with the Flood (Gen 7:1-24) and limits the lifespan of a human being to 120 years (Gen 6:3). The early biblical history of man is often met with skepticism; however, there are many points that substantiate the historicity of the biblical accounts.

Many prehistoric cultures have a myth about a flood, and two ancient tablet inscriptions attest to this: the Atra-hasis Epic (approx. 1630 B.C.) and the Epic of Gilgamesh (approx. 680 B.C), both of which can be seen at the British Museum. When examining these early accounts of a flood, only the biblical account has the possibility of being true.

The Bible records Noah's lifespan to be 950 years, and successive generations shorten thereafter. Scholars believe that the average lifespan for an Israelite at the time when the Pentateuch was written was less than 50 years old; however, the Bible records 4 generations of Jews from the time of entering Egypt to the Exodus (Ex 6:16-20), which implies a lifespan of at least 100 years. Contemporary records, with today's best nutrition and medical science, show that the longest living human being is around 122 years (Jeanne Calment).

After the Flood, Noah and his extended family grow and repopulate the earth until they are dispersed as a consequence of the city and tower of Babel (Gen 11:6-9). Such an account might be dismissed; however, the sixteen grandsons of Noah appear to be the basis of the naming many ancient nations many of which still exist today. The fact that all sixteen grandsons are listed and still significant today provides a basis of trustworthiness to the prehistoric account (see The Sixteen Grandsons of Noah).

Regardless of whether the Mosaic legislation was in place or not, Paul clearly indicates that everyone has the capacity for faith, because of the presence of a moral certitude. Faith though depended on what "law" one was obedient to.

All who sin apart from the law will also perish apart from the law, and all who sin under the law will be judged by the law. For it is not those who hear the law who are righteous in God's sight, but it is those who obey the law who will be declared righteous. (Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law. They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.) This will take place on the day when God judges people's secrets through Jesus Christ, as my gospel declares. (Rom 2:12-16)

Similar but not in reference to the law spoken of in the New Covenant (Jer 31:33), the phrase "requirements of the law are written on their heart" that Paul speaks of is the conviction or moral certitude of right and wrong that people have that makes everyone "a law for themselves."

Obedience to one's own personal conviction is seen in numerous biblical examples:

"… They turned aside quickly from the way in which their fathers had walked in obeying the commandments of the Lord; they did not do as their fathers (Jud 2:17).

"In those days there was no king in Israel: everyone did what was right in his own eyes." (Jud 21:25)

Obedience to God, which is the meaning of faith, is seen in Abraham (Gen 12:4; 15:1-6), and it is important to note that he was born and raised in a pagan family who worshipped idols (Josh 24:2).

Further evaluation of morals, its origins and whether it could be absolute, eventually leads one to logically conclude that morals and the definition of what is good is rooted in the character of God. God's absolute moral standard is not above Him or subject to capricious whim (see The Origin of Morality). It makes sense that when the Holy Spirit indwells in a Believer, the comparative figure of speech to the Ten Commandments written on stone would be to have the Law written upon the Believer's heart.

People after the birth of Jesus

As Jesus foretells of His death, He says, "And I, if I am lifted up from the earth, will draw all men to Myself." (John 12:32) Here Jesus speaks of drawing all men after His resurrection. Just as His Father had done, Jesus draws through love.

The Lord appeared to him from afar, saying, "I have loved you with an everlasting love; Therefore I have drawn you with lovingkindness." (Jer 31:3)

Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. We have come to know and have believed the love which God has for us. God is love, and the one who abides in love abides in God, and God abides in him. By this, love is perfected with us, so that we may have confidence in the day of judgment; because as He is, so also are we in this world. There is no fear in love; but perfect love casts out fear, because fear involves punishment, and the one who fears is not perfected in love. We love, because He first loved us. (1 John 4:15-19)

In abiding in God, Believers exhibit the fruit of the Spirit (Gal 5:22) which reflects to the world the character of Jesus Christ (John 13:35). A world without God is figuratively dark because of the selfish nature of human beings (Eph 4:18; 2 Cor 4:4); in contrast, Jesus' esteeming love of man through His atonement and God's forgiveness of sin is the light that is attractive to this dark world (John 12:46-47; 1 John 1:5-7). This is essentially how contemporary disciples accomplish the Great Commission (Matt 28:19-20; Mark 16:15-16). In this manner, Jesus draws all men, and because of His work of atonement, Jesus made it very clear that "no one comes to the Father except through Me" (John 14:6).

In the above context, it may appear that a person is lost if he does not meet a Christian or hears the gospel, but it is not so. The Jews, believing that one had to be taught in order to know God, were corrected by Jesus:

The Jews then were astonished, saying, "How has this man become learned, having never been educated?" So Jesus answered them and said, "My teaching is not Mine, but His who sent Me. If anyone is willing to do His will, he will know of the teaching, whether it is of God or whether I speak from Myself. (John 7:15-17)

In this passage, obedience is the key, and as Abraham exemplified in the Old Testament, obedience to God is the basis of faith.

The disciples discover a similar lesson:

John said to Him, "Teacher, we saw someone casting out demons in Your name, and we tried to prevent him because he was not following us." But Jesus said, "Do not hinder him, for there is no one who will perform a miracle in My name, and be able soon afterward to speak evil of Me. For he who is not against us is for us. (Mark 9:38-40)

John answered and said, "Master, we saw someone casting out demons in Your name; and we tried to prevent him because he does not follow along with us." But Jesus said to him, "Do not hinder him; for he who is not against you is for you." (Luke 9:49-50)

The individual casting out demons, according to both accounts, was unrecognizable by the disciples. Furthermore, when Jesus gives the twelve disciples the authority over unclean spirits (Mark 6:7) and sends them out in pairs, there is no mention of anyone else with this authority.

The unnamed disciple exhibits some characteristics worth noting: a) casting out was done by the power of God, b) the supernatural power to exorcise was not limited to the twelve disciples, and c) it was done in Jesus' name and as a testimony of Jesus' deity.

The Bible does not say how this disciple came to know Jesus; but, there is no doubt that he was a Believer. Because the twelve disciples sought to stop him indicates that he did not come to faith in their presence; thus, it is possible that one can come to faith and still know Jesus though it is not clear how. For Jesus, the explanation is simple:

He who is not with Me is against Me; and he who does not gather with Me scatters. (Matt 12:30)

But this should be understood in the context of Jesus' words to His disciples, "I am the way, and the truth, and the life; no one comes to the Father but through Me." (John 14:6)