The true Gospel is the Good News of the Incarnation, Life, Death and Resurrection of the Second Person of the Trinity, Jesus Christ. However, the question is “How can man be saved ?” And also “How can man be reconciled to God?” And also “How can man approach the likeness of God?” Which all approach the same question from different angles. As many of you know, the best way to examine the Good News to understand the Bad News. And so we begin at the Beginning.
The Triune God created the heaven and earth, ex nihilo, ultimately to show forth his glory. And man is created in his image and likeness and is in a state of sanctifying grace. Man is called by grace into a covenant with his creator; however, Adam sinned against God, breaking the covenant, seeking to be like God by his own efforts, without God. By our sin and rebellion, death enters into human history, for the wages of sin is death. He incurred original sin, that is to say, he lost sanctifying grace and original holiness that is required to enter into the Divine Life/abide in God’s presence/have fellowship with God. He also, as a result, has the stain of original sin i.e. sinful inclinations/concupiscience. However God in his sovereignty and timelessness had a plan of salvation that was first revealed as the Offspring of the woman who would strike the head of the serpent. God Himself would make a way. And so the Old Testament unfolds, covenant after covenant, showing a pattern, foreshadowing and pointing towards the ultimate sacrifice that God Himself would provide the solution to our sin.
In the Incarnation, the Second person of the Trinity took on human nature, being fully God and fully man, conceived by the Holy Ghost and born of the Virgin, in order to heal it but also to open the way so that we may share in the divine sonship and partake of the mystical life/be united to God/theosis/beatific vision.
In the Crucifixion He completes the sacrifice of the New Covenant which had begun when Christ instituted the Eucharist at Passover. In this one mystery, Christ the Paschal Lamb and Victim gives himself, the perfect, once and for all offering for the sins of the whole world. The one mediator between God and man. He died to atone for our faults and satisfy for sins. He descended into Hades to free the just, his redemptive work is for all men of all times. By death he trampled death and then on the Third day, he rises, glorified Christ the Victor by the power of the Holy Spirit.
In his earthly ministry Christ called people to repentance. He proclaimed a Kingdom not of this world, instituting a Church, upon Peter the Rock and the apostles. He left them with the promise that he would send his Spirit to teach all things. Before his Ascension he breathed on them,and gave them the authority to forgive sins. And afterwards the Holy Spirit Descended on them at Pentecost, fulfilling Christ’s promise, and initiating the birth of the Church. The Church becomes the guardian of the Good News, it is charged with spreading it, and teaching it. Not only that but the Church is the instrument for the salvation that Christ won through his death and resurrection. It is the means by which the Holy Spirit brings the dead man to life, allows man to be “born again of water and spirit” and initially justifies in Baptism (*not to get into a tangent but justification for the Catholic is not distinct from sanctification and we make distinctions between initial justification, which is entirely the work of the the Holy Spirit by grace through faith vs other justifications as the Christian grows in holiness. In addition, righteousness is not only imputed but infused/poured into us) , it is the means by which bread and Wine become the Body and Blood because “unless you eat my flesh and drink my blood you have no life in you”
The Gospel is the Good News of the New Covenant Christ has won for us through his death and resurrection. The new man is now a slave to Christ, under the Law of Christ. The Law of Christ is precisely what Christ tells us in the gospels: keep the commandments, feed the sick, clothe the poor, and it is summed up in the Beatitudes. It is not works of the law but rather, faith working through love that Christ asks of us in the Law of his New Covenant, because as you know faith without works is dead. And as the scriptures affirm again and again, we will be judged by our works.
*The new man is being made new through the Holy Spirit who is given by the Church in the sacraments, which are efficacious solely on the basis of the sacrifice of Christ*
We see the Church is not an arbitrary institution but a vital part of the salvation that Christ makes possible for us. It is both a visible and invisible reality, it uses visible signs to impart invisible graces. It is the Mystical Body of Christ, the New Eve, the New Jerusalem, the Bride of Christ, anxiously waiting for the end when the Bridegroom returns.
In summary: what is the Gospel? It is that Christ entered into human history, became the sacrifice of a New Covenant atoning for sins, and was resurrected, defeating death. He ascended but did not leave us stranded but left to the Church the Comforter, the Holy Spirit that is active in the sacraments. It is only when we partake of the sacraments as commanded by Christ and fulfill the obligations of the Law of Christ that we then walk in the Spirit. By partaking in Baptism, by the Holy Spirit we die to the flesh and are raised with Christ; we receive the sanctifying grace lost in the garden and in this we are “saved.” However we must “work out our salvation with fear and trembling” , cooperating with God’s grace so that “the God of peace himself sanctify you completely, and may your whole spirit and soul and body be kept blameless at the coming of our Lord Jesus Christ” . Those who endure to the end will be saved.