What is a doctrine?
The word “doctrine” comes from the Latin word doctrina, which means “teaching.”  (Doctrina comes from the Latin word doctor, meaning “teacher”).  A doctrine is a teaching which is presented for acceptance or belief.  From a Christian perspective, a doctrine is a teaching which defines who we are, what we believe, and what we ought to do.

Why are doctrines important?
Presbyterians believe that doctrines are a gift from God to the church.  Without doctrines—without sound teaching—it is quite unlikely that the church would have survived beyond the original apostles of Christ.  If any community (even the church—the community of faith) is to survive beyond any single generation, then it must concern itself with teaching.  In Scripture, we see that teaching grows the church.

So those who welcomed his [Simon Peter’s] message were baptized, and that day about three thousand persons were added.  And they devoted themselves to the apostles' teaching and fellowship, to the breaking of bread and the prayers.  (Acts 2:41-42)

Here, we see the apostles (as the early church) engaging in several ministries of the church.  First there is teaching, followed by fellowship, then sharing meals, and worshiping together.  The church is a teaching church, a welcoming church, a sharing church, and a worshiping church.  Teaching is not just one of the ministries of the church; it is a high priority of the church’s life and work.  Teaching can be seen as the church’s first ministry just as it was Jesus’ first ministry.

Teaching must be considered a high priority if we are to be faithful to Jesus’ great commission.  Concluding His time with His followers after His resurrection, Jesus charges His disciples:

“Go therefore and make disciples of all nations, baptizing them in the name of the Father, and of the son, and of the Holy Spirit, and teaching them to obey everything that I have commanded you.” (Matthew 28:19-20a)

Accordingly, being a disciple of Christ—being a faithful servant of our Lord—is being a teacher of Christian doctrine.

If you put these instructions before the brothers and sisters, you will be a good servant of Christ Jesus, nourished on the words of the faith and of the sound doctrine which you have followed. (1 Timothy 4:6)

Is belief in certain doctrines essential for salvation?
Although belief in Christian teachings is intimately and inseparably related to salvation, doctrines are not what save us.  We are not saved by knowledge, nor are we saved by what we have learned.  Rather, we are saved by our faith in God through Christ.

Therefore, since we are justified by faith, we have peace with God through our Lord Jesus Christ.  For if while we were enemies, we were reconciled to God through the death of His Son, much more surely, having been reconciled, will we be saved by His life. (Romans 5:1, 10)

Yet, when we say that we are justified, not by teachings, but by faith; we are articulating a doctrine.  Whenever we use words to proclaim our Christian faith to others, we are teaching Christian doctrines.  Doctrines are not our faith, but they are the articulation of that faith.  We can have a belief in doctrines; we have faith in God through Jesus Christ.

Isn’t faith and belief the same thing?
Although faith and belief are intimately and inseparably related, and although these words are often used interchangeably, they are not the same thing.  In the New Testament, the word pistis (πίστις) is sometimes translated as “faith.”  On other occasions, it is translated as “belief.”  Its meaning is often determined by its context.

In the second letter to the church at Thessalonica, for example, pistis implies cognitive acceptance of true teachings and is therefore translated as “belief.”

We must always give thanks to God for you, brothers and sisters beloved by the Lord, because God chose you as the first fruits for salvation through sanctification by the Spirit and through belief in the truth. (2 Thessalonians 2:13)

But, in Paul’s letter to the Romans, pistis implies trust in God as the One Who justifies ungodly persons and is therefore translated as “faith.”

To one who without works trusts Him Who justifies the ungodly, such faith is reckoned as righteousness. (Romans 4:5)

Accordingly, when we claim to have faith in God through Jesus Christ, we are making at least two affirmations.  First, we are specifically affirming that we trust God to be fulfilling His promises to us through the life and mission of His Son.  We are affirming that we trust God to be a God Who keeps His promises of forgiveness and love, of salvation and acceptance, of grace and mercy.

Second, we are, on a cognitive level, implying that we believe that God has promised forgiveness and love, salvation and acceptance, grace and mercy.  We are implicitly affirming that we believe that Jesus is the empirical demonstration of God’s love for us.

Presbyterians believe that God created His faithful people to live in community.  The Church is that community—the community of faith.  As a community, we share with one another the faith which we have in Jesus Christ.  We share with one another all of the joys and responsibilities which accompany this faith.  As a community, the faith which we share is inevitably expressed as our beliefs.  As we share our trust in Christ, we are teaching one another what we believe.  Thus, the common faith which we share becomes the Church’s doctrines which we teach and believe.

So, what must a Christian believe?
What must a Christian believe?  This is difficult to answer because Christians have not always agreed on which doctrines are to be taught and accepted.  For many centuries, Christians have striven to formulate those doctrines which would define what Christianity is and who the community of faith comprises.  The first official effort to establish definitive doctrines of Christianity was the ecumenical council at Nicea in 325 AD.  After revisions during a second ecumenical council at Constantinople (381 AD), the Church established the basic doctrines of what the community of faith teaches and believes.  These basic teachings were expressed in the form of a creed (from the Latin credo meaning “I believe”) which is known today as the Nicene Creed.

The Nicene Creed affirms the following beliefs:

We believe in one God,
the Father, the Almighty,
Maker of heaven and earth,
of all that is,
seen and unseen.  

We believe in one Lord, Jesus Christ,
the only Son of God,
eternally begotten of the Father,
God from God, Light from Light,
true God from true God,
begotten, not made,
of one Being with the Father;
through him all things were made.
For us and our salvation,
He came down from heaven,
was incarnate by the Holy Spirit and the Virgin Mary
and became truly human.
For our sake He was crucified under Pontius Pilate;
He suffered death and was buried.
On the third day He rose again
in accordance with the Scriptures;
He ascended into heaven;
and is seated at the right hand of the Father.
He will come again in glory to judge the living and the dead,
and His kingdom will have no end.

We believe in the Holy Spirit, the Lord and Giver of life,
Who proceeds from the Father,
Who with the Father and the Son is worshiped and glorified,
Who has spoken through the prophets.
We believe in one holy catholic and apostolic Church.
We acknowledge one Baptism for the forgiveness of sins.
We look for the resurrection of the dead,  
and the life of the world to come.  Amen.

Presbyterians, like most Christians, affirm the Nicene Creed as the most universally applicable articulation of what Christians believe.  This creed is a summary of our faith in God through Jesus Christ.

When Christians profess their faith in God, they are claiming to believe in one God Who is known in three persons (the Father, the Son, and the Holy Spirit).  Thus, Christians believe in the doctrine of the Trinity.

When Christians profess their faith in God through Jesus Christ, they are claiming to believe in a Lord Who is both God and human (Jesus Christ, the Son of God).  Thus, Christians believe in the doctrine of the incarnation.

When Christians profess their faith in the grace and power of God through Christ, they are claiming to believe in a Lord Who suffered, was executed, and was subsequently raised from the dead (the Passion of Christ).  Thus, Christians believe in the doctrine of the resurrection.

When Christians profess their faith in the redemptive mercy and compassion of God through Jesus Christ, they are claiming to believe in a God Who loves us despite ourselves and Who reconciles us to Himself through His Son (Jesus Christ, the Savior). Thus, Christians believe in the doctrines of atonement, of justification, and of sanctification.

When Christians profess their faith in the reconciling love of God through Jesus Christ, they are claiming to believe in a God Who reconciles us not only to Himself, but also to one another (the Body of Christ).  Thus, Christians believe in the doctrines of the church and of forgiveness.

When Christians profess their faith in the sovereignty and eternity of God through Jesus Christ, they are claiming to believe in a Lord Who reigns over us forever (Christ the King).  Thus, Christians believe in the doctrine of eternal life.