No person is a castle unto themselves, and further to the point, true faithfulness in any religion, necessitates the need and desire to see that other people are able to be co-beneficiaries of that faith. That is to say, there isn't any real good point in keeping to yourself, the very characteristics that enable you to be a good person; but rather, it is important to spread that faith to other people, that then allows those other people to live a better life and to be better people, themselves, and this then continues from one person to another.
So many people are reluctant to share their faith, because they themselves recognize that they are imperfect, perhaps deeply flawed, and additionally may have a past history that reflects that they have made some poor decisions. In addition, people are reluctant to share their faith, because they are not able to skillfully debate back and forth with another about the merits or even the most basic principles of their religion, because fundamentally that is something they don't have a clear understanding of; but, what they do know, is that their faith has changed the direction of their life, that their faith has improved their outlook, as well as their perspective, and all this has made them a better person for having that faith.
The thing about being a believer, though, is that it shouldn't be a secret, but rather it should be something, that is made known to others in conversations and interactions that naturally occur. That is to say, people are only too willing to share a successful diet result with one another, or tips on how to save money on insurance or other activities; so too, they should be willing to share with another, what has brought them peace and serenity to their being, so that they are now a more calm person, with a more generous spirit and heart. So that, when a given person, notices that change in one's personality, rather than being evasive about it, or elusive about it, it is far better to express in one's own way and one's own words, what it is that has helped to transformed you, for the better.
It is important to remember, that this isn't really about proselytizing or doing anything formal, per se, but it is more about when given the opportunity to allow other people to know who and what you really are, that the words that you then express, should actually honestly reflect that. Because your faith has changed you as a person, or has made you better as a person, you should be desirous of seeing that others have the opportunity and the benefit of hearing what you have to say, and seeing by your actions and demeanor, the fruits of that faith.
The only true faith is a universal faith, that is, it works in effect, for everyone, under all circumstances; therefore such a faith should be freely passed from one person to another, so that the whole body of people can truly benefit from it. Faith isn't really about the intricacies of any particular religion, but really it is all about recognizing the commonality that we all have via our creation by the very same Creator, and therefore our greatest duty is to treat our fellow people as our equals, deserving of the same respect, courtesy, and love, that we wish for ourselves.