"For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures," --1 Corinthians 15:3-4
The Bible teaches that God created the heavens and the earth. When he created them they were in a state of innocence and holiness. God made everything good.
God also created human beings, Adam and Eve, to be his image bearers. They were to serve God and live a life in perfect harmony with God. As image bearers they would exercise gracious care and tender rulership over all the creation.
God created human beings to be people who walk in fellowship with God and live in community with each other. When He created humans, he said they were "very good". He was pleased.
But things did not stay this way for long...
Fall into Sin
Human beings did not stay in their state of being "very good". In fact, the moment that humanity was put to the test in the garden, they failed. They failed to walk in God's way and in fact directly disobeyed God's command to them. This was sin.
The result of sin is that human beings could no longer enjoy God's company and walk with God in fellowship. Our communion with God was cut off, our sin separated us, we were no enemies. Even more, the creation we were to care over, God now cursed because we failed.
For the first time, death entered God's creation. It was no longer solely good. All people die now because we are under sin and live in sin from the very beginning of our lives. All of us are under sins curse which deserves God's wrath.
Cross & Resurrection
In the Bible, God reveals right from the beginning when man sinned, God began His great rescue plan to save people. He promised that He would one day send His own Son as a Savior. The Savior would reverse the curse of sin and usher in the end for which God always intended for human beings and creation.
The Lord Jesus Christ undoes the curse for our sins by becoming that curse for us (Gal. 3:13; Isa. 53:5-6). He dies on the cross, paying the penalty for our sin (Rom. 3:24-25; 1 John 1:9; 4:9-10). He took our place paying the guilt of sin so that in Him we might stand before God with righteousness (2 Cor. 5:21).
Jesus Christ then rose from the dead and was exalted up to God's right hand. He was given glory and honor so that He might rule over all creation (Eph. 1:20-23; Hebrews 2:6-10).
To receive salvation, we must place our faith in Jesus Christ and accept the gift that He has given us. A person believes in their heart and professes with their mouth that Jesus is Lord (Romans 10:9-10).
If we believe in Jesus Christ we become a new creation in Christ (2 Corinthians 5:17). God begins a new work in us and we can walk in fellowship with Him.
Our ultimate hope is not only heaven when we die, but the future resurrection. After Christ returns to earth and reigns over it, He will judge all wickedness. God will then make a new heavens and new earth. God will fulfill His original intent for human beings who have trusted in Christ. We will dwell with God and He will dwell with us (Revelation 21-22).