Theologian Kevin Vanhoozer:

Why does doctrine matter?

Primarily because without it, we could not answer Jesus’s question to his disciples, “Who do you say that I am?” (Matt. 16:15).

Christian doctrine sets forth in speech

  • who Jesus is (Christology),
  • why he had to suffer (sin),
  • how his death on the cross effected salvation (atonement),
  • how we relate to him (pneumatology),
  • how we benefit from his death (soteriology),
  • how the Spirit assembles the firstfruits of the new creation in Christ (ecclesiology), and
  • what happens when he returns (eschatology).

In order to say who Jesus is, we also need the doctrines of

  • God,
  • the Trinity, and
  • creation,

because his story does not start with his birth to Mary, but with his eternal fellowship with the Father in the Spirit and with all things being made through him.

Finally, because Jesus Christ is true God and true man, we also need to say something about the doctrine of

  • humanity.

Virtually every topic in systematic theology is necessary if we are to respond rightly to Jesus’s question.

— Kevin J. Vanhoozer, Hearers and Doers: A Pastor’s Guide to Making Disciples through Scripture and Doctrine (Lexham, 2019), xxii–xxviii. [My bullet points in the formatting.]