The gospel is the good news that Jesus Christ died for our sins and, in so doing, promised that we would have eternal life. The question is pertinent to the Old Testament, before the birth of Jesus when the gospel did not exist, and to the New Testament for those who may not have heard the good news.

Jews

With the benefit of their historical traditions, Jews were aware that human beings had a walking and talking relationship with God at the beginning of human history. With the disobedience of Adam in the Garden of Eden, sin was introduced, which broke the relationship between human beings and God (Gen 3:1-19; Rom 5:12). To restore this relationship, the Bible introduced some rituals necessary for atone for sin and make one holy to maintain a relationship with God. For example, Cain and Abel were recorded as making sacrifices (Gen 4:3-4).

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. like Cain's) must be paired with the animal offering (i.e. like Abel's) (Num 15:1-4).

Faith is the belief in the historical and real existence of the invisible God and placing a trust in His words and promises (Ex 19:4-6). The Mosaic Covenant taught what sin was (Rom 3:19-20) and instituted a procedure to atone for it so that God's people could maintain a relationship with Him. By acknowledging sin and removing it, one's relationship with God was restored.

Faith is determined by whether one believes and trusts in God. Complying to the Law of Moses, without a belief and trust in God, did not constitute faith.

Thus, Jews could have a genuine faith in God before the gospel was introduced. However, history showed that the nation of Israel chose to love the Law, added to it, and expanded it instead of agapē loving God and agapē loving their neighbor as God's kingdom of priests (Ex 19:6).

The prophet Isaiah warned the nation of Israel of their lack of faith and covenant infidelity. For their disobedience, the promised land would be taken away from them; however, in keeping with His promises to Abraham, a Savior / Messiah will be provided for them (Isa 53; Jer 31:27-34).

For any Jews who studied the Old Testament, Messianic prophecies would point to Jesus Christ and the gospel.

For those who had a genuine faith in God and were committed to their covenant obligations, the Holy Spirit would bring awareness of who the Messiah was. Simeon would exemplify this prompting by God (Luke 2:25-35), and an example of how God drew Old Testament Believers to His Son (John 6:44).

After Jesus Christ died and rose again, the historical act of His atoning sacrifice would be the basis of drawing all men to a saving faith through Him (John 12:32).

Gentiles

In the case of Gentiles, without a biblical tradition and knowledge of God, coming to faith was a different matter.

In one instance the apostles Barnabas and Paul speak to this (Acts 14:16-17), and to the church in Rome, Paul writes a similar message (Rom 1:18-23)

"In past generations He permitted all the nations to go their own ways; yet He did not leave Himself without witness, in that He did good and gave you rains from heaven and fruitful seasons, satisfying your hearts with food and gladness." (Acts 14:16-17)

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)

Here Paul indicates that God's invisible attributes are evident and clearly seen in His creation of the world and life. However, rather than worship God, many have chosen to worship idols and nature as the reason for creation of the world and life. Innately, mankind recognized a Creator.

God's creative acts can be viewed from a scientific perspective - there are at least 26 universal constants that enable the existence of the universe and life. These fundamental constants govern the laws of nature by describing the forces of interaction between atomic and non-atomic elements with a precise relationship and balance that enables life.

Any variance of these constants would not permit human DNA formation or the existence of water, or a habitable planet with oxygen, or a certain moon orbiting the earth, or an orbit around a certain sun or a certain universe.

At some point in life, virtually all human beings will consider at least one of these existential questions:

How was I created?

Why was I created?

How did I become moral?

What happens when I die?

Whether it is natural phenomenon or about one's origin, meaning, morality or end, the objective pursuit of these philosophical questions will lead one to God. Jesus' parables of the Hidden Treasure and the Costly Pearl touches on this very issue of the seeking man – one who was not looking and made a valuable discovery and another who was in search of something valuable.

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 (Jer 31:3), Jesus draws through love.

How does Jesus draw all men?

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)

When abiding in God, Genuine Believers exhibit the fruit of the Spirit (Gal 5:22) which reflects to the world the character of Jesus Christ (John 13:35). It is through the agapē love of others, that the world is drawn to Jesus Christ as represented by the Believer (John 13:35).

While the gospel is emphasized as the process of initial salvation (1 Cor 15:3-11), there are instances where it isn't clear. For example, the apostle John brings up an incident of a stranger exorcising in Jesus' name.

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).