Because this good news is authentic, we must first face reality. The eternal God of the universe is perfectly righteous and always acts in conformity with His character. We humans, on the other hand, fall short of God's standard of perfection. We are morally flawed - some of us worse than others! Our moral imperfection (sin) makes it impossible for God to have a relationship with us or to accept us into His perfect heaven. In fact, the opposite is true: His righteousness and justice demand that He find us guilty of moral imperfection and separate Himself from us eternally, which the Bible calls spiritual death.
To make matters worse, we cannot earn God's acceptance by following or keeping a set of religious rules or laws. We are simply incapable of being perfect. That's the reality of it. No matter how relatively "good" we are, we are just not good enough to satisfy God's righteous standard of perfection.
But there is good news! God is also loving and gracious and has provided a way for us imperfect humans to be accepted by Him without compromising His righteousness and justice. God sent Jesus Christ (the God-man) to accomplish this in His death and resurrection.
The heart of the good news is this: Jesus Christ died for us (in our place). On the cross Jesus voluntarily took our imperfections (sins) upon Himself and, as a result, suffered the consequences of those sins. God found Him guilty instead of us. God the Father then had to mete out to Jesus (God the Son) the just punishment for those sins, which was spiritual death. On the cross Jesus cried out, "My God, My God, why have you forsaken me?" It was at that moment that He bore the full penalty for our sins. As man, He was able to die for us; as God, He was able to bear the eternal consequences for sin, that is, being forsaken by the Father (which is the same as spiritual death).
Jesus' resurrection clearly demonstrated that He
was who He claimed to be - the Messiah, God in a human body. The resurrection
was also proof that God the Father accepted the death of Jesus as full payment
for our sins. Gods perfect righteousness and justice were satisfied. God could
then, consistent with His character, extend His love and mercy to us. He could
now forgive our sins and give us the gift of right-standing before Him, thereby
"saving" us from the consequences of our sins, namely guilt and spiritual death.
This is grace - God's undeserved blessing to us!