Start here at the Introduction: The Journey Begins
The Journey: Part 12 - What is it to walk by faith and in the Spirit?
In the very first verses of the book of Romans, Paul mentions the following,
Rom.1:17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
Through the next few chapters of Romans, we are provided great detail about our justification and spiritual sanctification. Essentially, Paul tells us what happens in the spiritual realm, the operations of God on our spirit, far out of reach from our workings and control. This salvation we receive is the "from faith" part. All we can do is trust that through the cross of Christ and through the operation of God, we are saved to the uttermost.