The carnal man is typically concerned only with forgiveness and with not having to pay the cost of his actions. There is little, if any, contemplation of what happens after forgiveness—or why God gives forgiveness in the first place. For its true significance to be understood, Jesus Christ's death must be seen within the context of all that God is working out. God is in the process of accomplishing much more than merely "saving" mankind or forgiving its sins!
God determined, even before Adam sinned and this present evil world was founded, that Christ, the Lamb of God, would have to be sacrificed for the sins of mankind (I Peter 1:17-21; Revelation 13:8). The present order of mankind rebelling against God was begun when Adam sinned in the Garden of Eden and was subsequently banished. The relationship with God was severed; man had no access to Him and eternal life, represented by the Tree of Life:
Then the LORD God said, "Behold, the man has become like one of Us, to know good and evil. And now, lest he put out his hand and take also of the tree of life, and eat, and live forever"—therefore the LORD God sent him out of the garden of Eden to till the ground from which he was taken. So He drove out the man; and He placed cherubim at the east of the garden of Eden, and a flaming sword which turned every way, to guard the way to the tree of life. (Genesis 3:22-24)
God knew what would happen if He allowed these now-tainted human beings to take of the Tree of Life also—they would live eternally, but because of their corrupt state, they would be eternally miserable. Therefore, God expelled Adam and Eve from the Garden, placing a flaming sword in the path to guard the way back to the Tree of Life. Mankind was cut off from God.
Two cannot walk together unless they are in agreement (Amos 3:3), and when Adam sinned he plotted the course for all who would follow after him—a course that had some good but also some evil. Humanity would walk a path that ultimately could only end in death, one that was definitely not in alignment with the life of the Eternal God. The prophet Isaiah explains this division that sin—the transgression of God's law (I John 3:4)—causes:
Behold, the LORD's hand is not shortened, that it cannot save; nor His ear heavy, that it cannot hear. But your iniquities have separated you from your God; and your sins have hidden His face from you, so that He will not hear. (Isaiah 59:1-2; emphasis ours)
Romans 6:23 explains how far sin separates man from his Creator: "For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord." Sin, being the opposite of all God stands for, causes the bitter harvest of death to be reaped. Yet, even though He is under absolutely no obligation to do so, God gives the gift of eternal life to pay the debt that every man incurs: the debt of his own, sinful life.
Most people believe that "eternal life" means "living forever." However, length of life is only one aspect of eternal life. If life were to continue forever without quality of life, it would be misery!
Paul tells us in Romans 6:23 that God's gift is eternal life, and in John 17:3, Jesus defines that gift further: "And this is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent." God's gift, then, is a life wherein a person knows—understands, has experience with—the Father and the Son. The gift is a life that not only stretches on forever, but also has a spiritual quality that makes such length of days desirable! That eternal quality—that perfection in living—has its only source in God, and a relationship with that supreme Source is only possible when man's sins, the cause of the great gulf between man and God, are atoned for. For this reason, God sent His Son to pay the debt of mankind's sins, so that man might know the Father and the Son in an intimate relationship, and be able to live life as They live.
But to what end? Why is God doing this? The gospel of John begins the explanation:
He came to His own, and His own did not receive Him. But as many as received Him, to them He gave the right [power; authority] to become children of God, to those who believe in His name: who were born [begotten], not of blood, nor of the will of the flesh, nor of the will of man, but of God. (John 1:11-13)
With the true acceptance of Jesus Christ—that is, receiving not only His sacrifice but also all of His teachings—come the power and authority to become a child of God! The eternal life that God gives as a gift is within the context of a family relationship. God plainly shows it is His purpose to increase His divine Family by bringing many children into it (Hebrews 2:10). Jesus Christ is actually the "firstborn" of many sons of God (Romans 8:29; Colossians 1:18).
The gospel Jesus brought to mankind is the "good news" of the Kingdom of God—and that Kingdom is dual. It is not only the ruling government that Christ will establish on earth when He returns, but it is also the Family of God—the God Kingdom composed of the spirit members of the God Family. Jesus taught that humans can be "born" into the Family, or Kingdom, of God (John 3:3-8).
There are only two full members in the God Family or Kingdom at the present time—God the Father and Jesus Christ, the firstborn Son. Christians are likewise a part of that Family, though not complete until they are likewise composed of spirit, through being resurrected (or changed, if they are still alive when Jesus Christ returns to establish His Kingdom on earth; see I Corinthians 15:50-52; I Thessalonians 4:14-17).
This, then, is why God has provided a way for the separation between Himself and man to be removed through the atoning sacrifice of His firstborn Son. God is creating man in His image and likeness (Genesis 1:26). The death penalty incurred by the sins of mankind had to be paid to make possible God's great purpose of bringing many sons to glory. Without the removal of the defilement of sin, God the Father could not walk in agreement with His children.