Romans 8:28-30 is a very helpful section of scripture. If you are trying to understand this very important doctrine you must remember that the term salvation is used in different senses. Language and theology must be precise. At times salvation can refer to justification (which comes through faith in Christ alone).
Salvation in a broader sense has to do with God's electing grace to choose, justify, sanctify, and finally glorify.
Have a great day!