Repent and Believe the Gospel
After THE Baptism, that is Jesus baptism where He identifies with us sinners by getting into the waters – here the Word (Jesus) is added to the waters to purify them and all who enter. Sins washed away, cleansed by the holy One of God. After THE Temptation of Jesus by the ancient serpent (the deceiver, the father of lies, Satan himself); Jesus does what Adam (son of God) and Eve could not do; what the children of Israel (sons of God) could not do; what you and I cannot do – He defeats the devil by not falling into temptation. Mark now records for us what Jesus says about repentance and belief:    
 
Mark 1:14 Now after John was arrested, Jesus came into Galilee, proclaiming the gospel of God, 15 and saying, “The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.”
 
“The time is fulfilled, and the kingdom of God is at hand” – The Kingdom of God is here with Jesus presence. The promised One of the Old Testament is found in Jesus fulfilling. The Kingdom is here and we are living in the End Times right now in His coming (but that is for a longer discussion at another time).
 
Christian Repentance
Christian repentance is not merely feeling bad about our sins (as Judas). Instead, Christian repentance involves:
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• First a recognition that however I may have sinned against other human beings, my offense is first and foremost against a righteous God. There is appropriate sorrow and regret.
• Second, I seek and trust in the full forgiveness which I have because of Christ’s life, death, and resurrection.

 
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Where is this written? St. Paul writes in Romans chapter six: “We were therefore buried with Him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.” (Rom. 6:4) [Small Catechism, Baptism, Fourth Part]
 
Rising to new life in Christ through Baptism involves two major issues.

• First, I embrace the new life I have received in Baptism. That is, I flee from sin and instead devote my time and energies to the good works to which all Christians are called. This change in behavior is neither to diminish the wickedness of my sin nor to earn God’s forgiveness. Rather, I live righteously because that is who I am (or more to the point, who God has made me in Baptism).
• Second, as a baptized Christian, I also live in the certainty of forgiveness and eternal life. I have certainty because my Baptism is not based on my merits or behavior but rather on God and His promises found in His Word. Baptism is the source of ever-present grace each day and the joyful anticipation of Christ’s return and life eternal with Him.

Matthew 16: 13-16 (ESV)
13Now when Jesus came into the district of Caesarea Philippi, he asked his disciples, “Who do people say that the Son of Man is?” 14And they said, “Some say John the Baptist, others say Elijah, and others Jeremiah or one of the prophets.” 15He said to them, “But who do you say that I am?” 16 Simon Peter replied, “You are the Christ, the Son of the living God.”
 
Is Jesus Moses; Elijah; some other prophet; John the Baptist; a great moral teacher; a life coach; an example; as “people” claim? Is Jesus someone who speaks God’s Word and points to a Savior, or is He God’s Word and is He the Savior?
 
The Son of Man identifies with us as brothers and sisters, born of a woman, with the vocation of a man. Yet Son of Man also points back to Daniel 7:13-14, with the vocation of an omnipotent God with an everlasting kingdom.
 
All of Christianity revolves around how one sees this Son of Man – Jesus (Yahweh saves) Christ (The Anointed One; as prophet, priest, and king), the Son of the living God – Peter’s answer.
 
“What is the Christian faith?” an: The Christian faith is the confession that Jesus Christ is the world’s only Savior and Redeemer (John 14:6; Acts 4:12, 1 John 5:11-12).
“What is Christian?” an: A Christian is someone who, by the power and work if the Holy Spirit through the Word of God, believes in and confesses Jesus as Savior and Lord. Through Baptism, a Christian is adopted into the Father’s family, the Church (Romans 8:15, and 10:10; 1 Corinthians 6:11, and 12:3).
2017 CPH Luther’s Small Catechism with explanation
 
Matthew 16: 17 (ESV)
17 And Jesus answered him, “Blessed are you, Simon Bar-Jonah! For flesh and blood has not revealed this to you, but my Father who is in heaven.
 
Simon, Bar-Jonah (son of Jonah) vs. Son of the living God. Jesus is not just flesh and blood (Son of Man) like others born in this world, but existed before the creation of the world. And He now says “Blessed are you…you have a wisdom that far exceeds anything in or of the world – no man’s imagination, no world religion, no works of man - but from the very God Himself revealed to you through and in His Word made flesh (God incarnate – Jesus) and/or His written Word (Jesus), by the Father through the Holy Spirit. This is the peace that surpasses human understanding.