Which way around?
Which is true? What we believe is shaped by our lives, or our lives are shaped by what we believe? The letters of the apostle Paul begin with theology and move to practice, and for this reason we tend to think that you begin with theology, doctrine, belief and this then shapes your life.
And certainly, you would want, with say a new believer, to get their doctrine straight praying that new life would flow out of that, in response to truth and in obedience to the commands of Christ.
The missing step - Paul's theology was written in blood
The missing step in this train of reasoning is this: the person who wrote that theology in the first place, lived a life of suffering, trouble, persecution and heartache (always shot through with holy joy, of course). Paul walked in the steps of his Master, the man of sorrows acquainted with grief. Paul did not write theology from an armchair (or any other kind of "chair"), but from gutsy front-line back-breaking, heart-aching ministry. His theology was written in the trenches. And so was every other NT author. In other words the theology we have to pass onto the saints was itself forged in extremis.
An illustration (not theoretical)
Here's an example. Take a group of Christians who live for pleasure (I know this is an oxymoron, but Paul says somewhere that many live as enemies of the cross). They spend their free time, as the world does, caught up in hobbies, holidays, families, pleasure. These "saints" (on the last Day, they may be called goats rather than saints, if I understand Matthew 25 correctly) get together for a home group and decide to study the Bible together.
Let's watch: how will their (easy) lives affect their theology?
(1) The will avoid all talk of the cross. Oh I don't mean the cross of Christ, they are likely to revel in what JESUS SUFFERED FOR THEM (and they will know that talk of the cross is an essential to orthodoxy). No, I mean, the calling of the Christian to take up their crosses, to suffer for his sake. A veil will cover their eyes as they read such verses.
(2) They will resist all teaching that challenges them to serve the world in sacrificial love. Called to love our neighbours? They'll find clever reasons why that command no longer applies (if they didn't they might have to give up a hobby, or a weekend with the family, horror of horrors!)
(3) They will resist the idea that the mission of the church is to reach the lost. Jesus was only speaking to his disciples in Matthew 28 (No, seriously, I have met such people!). I mean, if Jesus meant us - them - to reach the lost, we'd have to give up an evening's pleasure: Joking aren't you?
(4) They will judge the churches. Most seriously of all, they will judge their brothers and sisters in other churches whose hands and feet bear wounds, who work hard, who serve Jesus.
Our theology, you see, does follow life.
Don't pay attention to armchair theologians. And now you know why the names of Luther, Calvin and Spurgeon will live on (they wrote their doctrine in the sweat of ministry) while so many of the Big Names and Big Authors of today will be forgotten ere before they die.