Whether or not one can rightfully call a person's faithfulness a virtue depends in part on the object of that person's faithfulness.
Conclusion
Whether or not one can rightfully call a person's faithfulness a virtue depends in part on the object of that person's faithfulness.
Evidence
Virtues are supposed to be praiseworthy, but faithfulness isn't always praiseworthy (for example, you could be faithful to hating / resenting someone, and no one would call that virtuous).
Evaluate
Whenever we read Main Conclusion or Role, we start by thinking
If we go into these paragraph thinking, , it makes it easier to interpret what's going on.
Does the first sentence present as though it's our Author's Opinion? Yes, somewhat. It says "rightfully", which is an opinionated term.
Does the author proceed to try to defend / support that opening claim? Yes, the author gives an example of faithfulness that isn't a virtue, to support his claim that whether or not a certain faithfulness is a virtue depends on other factors.
Goal
Once we've correctly found the Conclusion, the hard part is done. We're now just picking whatever answer best matches the meaning of the first sentence.