Let’s review. Jesus Christ is our mediator. He is one hundred percent God and one hundred percent man. He is one hundred percent God because he must be able to bear the brunt of God’s wrath for his people. He must also be one hundred percent human because only a human can pay for human sins. He is also one hundred percent righteous, which means he has no taint of sin and can therefore pay for sins perfectly. Jesus came to “save his people from their sins” as foretold by the angel.  But who had their sin paid for on the cross? For whom did Christ die? And how is this sacrifice applied?
20.Q: Are all men, then, saved by Christ just as they perished through Adam?
A: Only those are saved who by a true faith are grafted into Christ and accept all his benefits.
Q: What is true faith?
A: True faith is a sure knowledge whereby I accept as true all that God has revealed to us in his Word. At the same time it is a firm confidence that not only to others, but also to me, God has granted forgiveness of sins, everlasting righteousness, and salvation, out of mere grace, only for the sake of Christ’s merits. This faith the Holy Spirit works in my heart by the gospel.
Q: What, then, must a Christian believe
A: All that is promised us in the gospel, which the articles of our catholic and undoubted Christian faith teach us in a summary.
23.Q: What are these articles?
I believe in God the Father almighty,
Creator of heaven and earth.
I believe in Jesus Christ,
his only-begotten Son, our Lord;
he was conceived by the Holy Spirit,
born of the virgin Mary;
suffered under Pontius Pilate,
was crucified, dead, and buried;
he descended into hell.
On the third day he arose from the dead;
he ascended into heaven,
and sits at the right hand
of God the Father almighty;
from there he will come to judge
the living and the dead.
I believe in the Holy Spirit;
I believe a holy catholic Christian church,
the communion of saints;
the forgiveness of sins;
the resurrection of the body;
and the life everlasting.
Christ’s sacrifice was given only for those who are grafted into him by true faith. Jesus’ sacrifice was not all-inclusive as the Universalists claim—that all of humanity, regardless of belief, has peace with God. No. Jesus’ sacrifice is only applicable to the one who cries out in true faith. We will forgo the discussion of “who will have true faith” for now, but suffice it to say, the question is relevant and important given that the Catechism recognizes that humanity is dead in sin, inclined to all evil, and unable to express saving faith outside of regeneration.
What is true faith? It is three things working together: The acceptance of what God has revealed in his word as truth, a firm confidence in the sacrifice of Christ on your behalf and all the benefits that are given to you out of sheer grace, and the working of the Holy Spirit in your life—both regeneration and what is called progressive sanctification. That is to say, your life changes, or as the Westminster Standards puts it, an “endeavor after new obedience.” Let us examine each one more closely.
A sure knowledge:
The testimony of the Scriptures is that one can know, for sure, that they are saved. God is not playing around with us. This is not a game. God has promised that all who call on the name of the LORD, confessing with lip and heart that Jesus is lord and that God the Father raised him from the dead, will be saved.  God keeps his promises and we are obligated as His creatures to believe them.
A firm confidence:
Not only does the Christian mentally ascent to the promises of God found in Scripture but we also have confidence that the promises of God are yes and amen for all those who cry out to him. Take the Sacraments for example; they are visible signs that signify spiritual realities. In baptism, we are promised that Christ has washed us as surely as water washes dirt from my body. At the Lord’s Table, we are told that Christ nourishes and sustains us as surely as bread and wine nourish and sustain the body.  IF we can be so sure of these physical things, then the confidence in God’s promises are surer than these.
The work of The Holy Spirit
Faith is not some abstract thing that sits on a shelf. True faith is something real and vibrant that works out into a person’s life. A person who has a sure knowledge and firm confidence in God’s promises will show this evidence in their life. This is not to say that there is a bar to clear in the Christian life as if the Christian life is a checklist of achievements. What this does mean, however, is that because the Spirit dwells in you, you will begin to bear the fruit of repentance and obedience as an evidence of your justification. The Westminster standards calls this an “endeavor after new obedience” precisely because the same Spirit that raised Jesus from the dead now resides in each and every believer. There is no cookie-cutter pattern for this “newness of life” – it will be different for each person and there will even be seasons within the same believer but the goal for God’s people is the same: Christ will present us all blameless before the Father. 
So what must a Christian believe? What is the faith once delivered to all the saints? Is there an answer to this? Yes. The Christian must believe the Gospel. The Church has historically expressed this standard in the historic, ecumenical creeds starting with the Apostles’ Creed. The Apostles’ Creed is the line in the sand, only it isn’t sand. It’s an inerasable, unmovable line etched in an indestructible metal like Adamanium; if you leave the Creed than you leave the faith.
I believe in God, the Father almighty,
creator of heaven and earth.
I believe in Jesus Christ, his only Son, our Lord,
who was conceived by the Holy Spirit
and born of the virgin Mary.
He suffered under Pontius Pilate,
was crucified, died, and was buried;
he descended to hell.
The third day he rose again from the dead.
He ascended to heaven
and is seated at the right hand of God the Father almighty.
From there he will come to judge the living and the dead.
This is what you are obligated to believe, Christian. You cannot compromise on any of these articles of faith. The Creed is divided into three parts and each article has implications which we will explore more next time, on @TheologyMix.
Calvinist Coulson -Phil is a confessing member in the United Reformed Churches of North America (URCNA) and holds a Bachelor of Theology. He and his wife are quietly saving the world while shepherding their three children. Follow him on Twitter at @XpCoulson.