There is a way that seems right to a man,
but in the end it leads to death
Prov 14:12 NIV
Therefore, since the children share in flesh and blood, He Himself likewise also partook of the same, that through death He might render powerless him who had the power of death, that is, the devil, and might free those who through fear of death were subject to slavery all their lives.
Heb 2:14-15 NASU
In the beginning, there was no death. God, the creator of all things, is not the author of death, but of life. The testimony of scripture is that "He gives to all life, breath, and all things."(Acts 17:25), and "in Him was life, and the life was the light of men."(John 1:4), and "God is light and in Him is no darkness at all."(I John 1:5), and "no spring can yield both salt water and fresh."(James 3:12). Since God is the author of life, full of light, death had to come from some other source rather than directly from God. The source of death and its mechanism are explained by Paul in Rom. 5:11, "through one man sin entered the world, and death through sin, and thus death spread to all men." Death is the product of sin, and neither sin nor death originate with God, but both exist in opposition to Him. "For all that is in the world - the lust of the flesh, the lust of the eyes, and the pride of life - is not of the Father but is of the world. And the world is passing away, and the lust of it; but he who does the will of God abides forever."(I John 2:16-17). In the beginning, God created life and a means for its continuity (Gen. 2:9, 3:22-23), but when man chose rebellion and death, the means to sustain physical life forever was removed from man's reach. Man, by sin, had changed the nature of his own existence, had chosen the way of death (Prov. 14:12) and brought new physical and spiritual rules into being, to his own detriment.
To understand how things could exist in this world (or anywhere) that are not from God (such as sin, death, and the causes of sin mentioned above), we should note that man was given great authority by God within the creation. Man was given authority over the earth and every thing that lives in it (Gen. 1:26), but he abdicated his authority, yielding it up to the serpent, later identified as Satan. Satan was already apparently a creature with great power and authority, but man gave Satan authority in this world, by choosing to obey him rather than God, and that action brought death into being by the authority of man, as God had warned. Although it was man's God given authority that brought death into being, and caused the creation to be subjected to futility (Rom. 8:18ff), the very act of obedience to Satan him power through the death that came into being (Heb. 2:14-15). Thus Satan gained power over man through death and the fear of death. Death, and all that goes with it, was brought into being in direct rebellion against God, and came under control of Satan, so that Satan is the one who "had" the power of death, while man was "subject to bondage", rather than having all things subject to himself, as he was made to have them (Heb. 2:6-9).
Closely aligned with the existence of death in scripture is a place where the souls of the dead went to wait, called sheol in Hebrew or hades in Greek. Much confusion has resulted from the fact that these words are not consistently rendered into English, sometimes being transliterated (printed as sheol or hades), sometimes being translated "the grave", "the pit", or even "hell". Sheol is often spoken of in the Old Testament, and is identified as the place a soul would go in death (Ps. 30:3, Job 33:18,22,24,28,30). Generally, sheol is not spoken of with joyful expectation and is sought only by those whose suffering is extreme (note Ps. 89:47-48, Ps. 49:14-15, II Sam. 22:5-6, Ps. 86:13, Ps. 116:3-4). Many of the passages that speak of sheol carry the hope of being released or redeemed from it, rather than a longing to be there. Ps. 49:8-9 raises the hope that there could be a redeeming price paid that would free a soul so that it might not even "see the Pit", but rather "continue to live eternally". When Old Testament king Hezekiah anticipated death he fully expected to be parted not only from this world, but also apart from God and unable to praise Him (Isa. 38:9-20). Though he was a righteous man (38:2-5), Hezekiah had no joy at the prospect of death, no eagerness to be in the "pit", in sheol. Hezekiah had no thought that he would die and be with the God he served; rather he expected that in death he would be apart from God and unable to serve. Other righteous individuals shared this Old Testament perspective as well (Ps. 6:5). Jesus Himself pictured Hades as a force to combat, an obstacle to be overcome, when He told the disciples that He would build His church and "the gates of Hades will not prevail against it." (Matt. 16:18). We know that when He died Jesus' soul, like the soul of Hezekiah and David and all others who lived from Adam to Christ, went to Hades (Acts 2:25ff, esp. 27 & 31). However, over Him Hades did not prevail, He went in and came back out again, the firstfruits from the dead (I Cor. 15:20, Rev. 1:5). Hades was not where He wanted to be, and He didn't stay there, but rather "He ascended up on high, He led captivity captive, and gave gifts to men."(Eph. 4:8). Whereas Hades had held all men since Adam captive, in bondage, Jesus led captivity captive. He took charge of the keys of death and Hades (Rev. 1:18) and reclaimed the position Adam had abdicated. Jesus is the Man who now has all things in subjection to Himself (Heb. 2, Rom. 5, I Cor. 15).
Before the work of Jesus to reclaim what Adam had lost, Satan "had the power of death" (Heb. 2:14-15), but through His own death Jesus took that away and destroyed the devil's work (I John 3:8). Jesus came to do this, and was successful in His efforts (Rom. 5:18, I Cor. 15:21). Before the cross, Satan had the power of death. After the cross, the keys of death and Hades are in Jesus' hands, and the gates of Hades do not prevail against Him or His kingdom. While the Old Testament and the events of the gospels (prior to the finished work of the cross) looked forward to the reconciliation of man and God, the epistles tell us that Jesus has now made reconciliation and "made peace through the blood of His cross". Jesus has revised the rules that man let Satan impose upon him. The anticipated reconciliation of things on earth and in heaven is now a reality and is the basis of our approach to God (Col. 1:21-23). Jesus' death has changed our relationship with God, our relationship to sin, and our relationship with death. He has changed everything that matters about our future so that we have a real choice both about where we are and where we are going.