Lying for Jesus ... Again

[StuartJ]

Several of us here have accused persons of faith of lying by omission.

Is omitting things that don't fit your faith a sin ...?

[janavoss]

In light of recent events, I thought I'd bump this one up the list for further comment.

I have great difficulty trusting people of faith when it comes to matters of faith.

1 Peter 2:1
1 Therefore, rid yourselves of all malice and all deceit, hypocrisy, envy, and slander of every kind.

Psalm 101:7 English Standard Version (ESV)
7 No one who practices deceit
shall dwell in my house;
no one who utters lies
shall continue before my eyes.

Colossians 3:9-10 ESV / 81 helpful votes Helpful Not Helpful
Do not lie to one another, seeing that you have put off the old self with its practices and have put on the new self, which is being renewed in knowledge after the image of its creator.

It seems you have some particular examples in mind which you have not shared here, so I don't really know what you're going for. However, a simple answer to your initial question:
Is it sin to intentionally attempt to conceal something for selfish reasons - yes.
What if it's a matter of ignorance - no, they didn't know any better. However, they should be open to learning something they did not know before.
Are there times when it is more appropriate to keep one's mouth shut, even if something is the truth - yes, of course, but depends the motive. I cannot think of an example where it would be better to keep one's mouth shut in matters of faith, as you say, but again I don't know what you are referring to.