Does Isaiah 58 refer to the modern church or past Israel? Does it have anything to do with reward that the church will receive (Crown)?
Like we do with all of God’s word, we should read Isaiah 58 listening for whatever lessons the Lord desires to speak into our hearts, and I think there’s plenty there for us.
But in the literal sense the chapter was addressed to Israel, who were commanded to fast on certain Holy Days and keep the Sabbath. It’s clear that the Lord was reminding them that it was the motive of their hearts when doing the things He commanded that counts with Him, not just the performance of the physical action. That lesson is certainly as applicable to believers today as it was then.
Parts of the chapter (esp. verses 12-14) found partial fulfillment after 1948, but also speak of the Kingdom Age.