If you are a UK resident watching Revelation TV live in the UK, you require a TV license in order to watch Revelation TV.
This is true regardless of how you watch the channel.
However, if you only watch Video-on-Demand/Catch-up programmes using Revelation TV App/ROKU/Smart TV and do not use the Live option you may not need a license. In this case, we would suggest that you check with the TV licensing authority. You can find out more at http://www.tvlicensing.co.uk