I think it depends on the design. Inntrest is something that can be drawn upon by visualisation itself. I think a black t-shirt with a white cross would be a bit too simple. It could work, but I think it would be too simple. I don't think it would co-respond too well with the secular market.
Now, it got some brown sorta grunge paint on parts of the sides where the arms are. Kinda hard to see, but it fits the image. A fake white t-shirt on the top. *It only covers that region which is shown. Cross with a faint silver light, slightly gothic design. Fits with an open sweater. Draws enough attention from the secular side to look inntresting.
Then again, clothing probably is not going to do much good in the long run. I'd rather have a brand who sent subtle messages on cool designs that could break into the market. There is even a passage in the bible that tells one not to worry about what to wear if I recall things correctly. Deeds speak tenfold to design when it comes to the christian message. And although I'd love to see a christian brand break into everything from clothing, film/series and games. It would however have to be deserved, the quality would have to match up with the secular side of the market. Now aside from some music regions, the christian market has generally failed to get too much secular inntrest and mostly so because of lack of quality. Effort I cannot comment on, but it matters little if the quality is lacking.