v. 16-17 For I am not ashamed of the gospel; it is the power of God for salvation to everyone who has faith, to the Jew first and also to the Greek. For in it the righteousness of God is revealed through faith for faith; as it is written, "The one who is righteous will live by faith."
These two verses at the beginning of Paul's letter to the Romans are a summary of it, and, indeed, of Paul's way of understanding what God has done in Jesus Christ.
It's all about faith. Any other words we use, like "salvation" and "righteousness" cannot be understood apart from faith. Faith is the power of the gospel.
The nearest synonym to faith is "trust." Trust is something a few of us do easily, but for many of us it is very hard. We have learned to be suspicious over the years, sometimes for very good reasons.
I wonder, though, if faith precludes suspicion, or even doubt. Somehow I think they are a part of it. Faith is not, after all, certainty. If there were some proof of God's existence, for instance, faith would be unnecessary. But the Bible starts with the biggest faith statement there is, "In the beginning God..."
Our suspicions and our doubts are somehow, mysteriously, a part of our faith. Faith is always "in spite of of all evidence to the contrary." If we haven't considered the contrary then we cannot know faith. We cannot make the choice for faith if we do not consider the opposite choice we might make. Then it is a choice of which we need not be ashamed.