When human beings came into existence as rational and moral beings endowed with free will, aware of the realities of truth and love, they simultaneously became capable of knowing Love Himself: this is part of what it is to be made "in the image of God". God who had designed and caused this to be, immediately revealed Himself to the first such beings in His image. For a while they enjoy a simple yet well-provided for existence physically, and are spiritually nourished and protected by their unhidered relationship with God.
The Bad News, Part One
But, early in the relationship, Mankind chooses to reject God, breaks communion with Him, and tries to become his own god. From this pride, rebellion and self-deception come the corruption of human nature due to its disconnection from God and loss of the supernatural blessings of this relationship. Humans continue to seek short-term pleasure over long-term happiness and continue to undermine their specifically human dignity and purpose by allowing animal instincts to rule over the reason and will, rather than the other way around. They keep a life of the body and soul, but have lost the spiritual life which alone could inspire and strengthen their will and safely order their reason.
Therefore man cannot consistently love God or neighbour from the heart and is lost in selfishness.
The Good News, Part One
God, being Love, wants to rescue us from our evil and bring us back into fellowship and friendship with Him. By word and deed He reveals to and through a chosen portion of humanity (a particularly oppressed portion: the descendants of Abrahaam, the Israelites) His Love and the way of love and goodness. He does this through patriarchs and prophets (his messengers to his people), rescuing the chosen people from oppression, specially providing for them, and by the restraining discipline of the Law.
The Bad News, Part Two
His people continue to reject Him more often than not, and fail in their calling to be a witness to the nations of God's goodness and truth.
The Good News, Part Two
But God knew their weakness -- the weakness of all humanity -- and so, having prepared the way using prophets and the few other faithful ones, he comes down to our level, given we are not capable of reaching up to His. God the Son takes human nature upon Himself as part of a plan to restore us to the divine family, giving us a share in his relationship with the God the Father in the power of God the Holy Spirit.
In this Incarnation ("becoming flesh") God in the person of Jesus restores our human nature by taking it on Himself and absorbing the terrifying consequences of our sin (as seen in the suffering and death of his torture and crucifixion by the Jews and Romans of 20 centuries ago) without, of course, being or becoming sinful. At the Cross we see the collision of pure, forgiving love with pure, hating evil. Thus, on the Cross, Jesus Christ overcomes the evil in us on our behalf: and with his divine life overcomes human death in the Resurrection. His act of perfect, self-sacrificial obedience fulfils God's holiness and righteousness and has the power to undo and reverse our disobedience and its results.
This victory is a victory for all of us, if we will only accept and receive it by saying "yes" to God's offer of love and mercy. We do this by joining ourselves in loving trust to Jesus as our Lord and Saviour, as our very Life -- and carrying this "yes" to God through our lives.
The final result is reunion with God forever, as the free gift we have accepted is in fact the Life of God, the Holy Spirit, who is able to make us share in the Resurrection of Jesus.