God is infinitely holy. Nothing short of holy enters His presence. We are by nature completely sinful people, unable to approach the holy God because His wrath rests on us. No one can approach God with good works, piety or self-produced righteousness. The wrath of God was satisfied, once and for all, on the cross, through the atoning sacrifice of His Son, Jesus Christ. The righteousness God requires was performed by Christ alone and imputed to those who believe, that they may be declared righteous in God's sight, not on the basis of the righteousness produced in the believer by God, but on the sole basis of the righteousness of Jesus Christ.
God created us for a relationship with him - to love him and be loved by him; to worship him and to glorify him. Because of the fall of man into sin, we could no longer have that relationship with God. Our selfishness, our pride, our hatred, our greed and all our sins get in the way of us knowing God personally. And this is not just for this lifetime, but potentially eternally. We deserve not to be with God or enjoy God, but to bear His righteous judgment.
The heart is deceitful above all things, and desperately sick; who can understand it? - Jeremiah 17:9
But each person is tempted when he is lured and enticed by his own desire. - James 1:14
Now we know that whatever the law says it speaks to those who are under the law, so that every mouth may be stopped, and the whole world may be held accountable to God. - Romans 3:19
For as by the one man's disobedience the many were made sinners - Romans 5:19a
For all have sinned and fall short of the glory of God. - Romans 3:23
For the wages of sin is death - Romans 6:23a
Whatever does not proceed from faith is sin - Romans 14:23
Salvation is not something we are able to will and produce in and of ourselves. It is not us choosing to accept God's grace, since in our completely depraved, sinful state we cannot hope to do so. It is God's grace overcoming our resistance to His grace. In our fallen human nature, we always use our freedom to resist God. Only God can overcome that rebellion in our hearts, something we are powerless to do.
For while we were still weak, at the right time Christ died for the ungodly. - Romans 5:6
But God shows his love for us in that while we were still sinners, Christ died for us. - Romans 5:8
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. - Ephesians 2:8-9
In our state where we could not save ourselves, God reached down to save us by His grace alone. Christ became the substitute or propitiation for our sins. But taking away sin alone does not merit anyone eternal life in God's presence. We do not enter heaven with a zero balance. Only perfect righteousness enters His presence. Christ performed that perfect righteousness for us, and that righteousness is imputed onto us, and through that, we are justified before God.
Christ redeemed us from the curse of the law by becoming a curse for us--for it is written, "Cursed is everyone who is hanged on a tree" - Galatians 3:13
For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek. For in it the righteousness of God is revealed from faith for faith, as it is written, "The righteous shall live by faith. - Romans 1:16-17
Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal life. He does not come into judgment, but has passed from death to life. - John 15:24
If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. - 1 John 1:9
There is therefore now no condemnation for those who are in Christ Jesus. For the law of the Spirit of life has set you free in Christ Jesus from the law of sin and death. For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit. - Romans 8:1-4
Salvation isn't a free ticket to live however we used to live. Christians are being regenerated - completely changed. A new life, a new creation, born again, into a new and living hope. The focus changes from self-glorification and self-reliance to God-glorification, finding fulfillment in Christ. This change is part of a lifelong process, carried out by God's grace, into eternity.
So, whether you eat or drink, or whatever you do, do all to the glory of God. - 1 Corinthians 10:31
Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us, looking to Jesus, the founder and perfecter of our faith, who for the joy that was set before him endured the cross, despising the shame, and is seated at the right hand of the throne of God. - Hebrews 12:1-2
And by this we know that we have come to know him, if we keep his commandments. Whoever says "I know him" but does not keep his commandments is a liar, and the truth is not in him, but whoever keeps his word, in him truly the love of God is perfected. By this we may be sure that we are in him: whoever says he abides in him ought to walk in the same way in which he walked. - 1 John 2:3-6
And so, from the day we heard, we have not ceased to pray for you, asking that you may be filled with the knowledge of his will in all spiritual wisdom and understanding, so as to walk in a manner worthy of the Lord, fully pleasing to him, bearing fruit in every good work and increasing in the knowledge of God. - Colossians 1:9-10
And we know that for those who love God all things work together for good, for those who are called according to his purpose. For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers. And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified. - Romans 8:28-30