“How can Matthew 5:12 talk about rewards in heaven for kingdom saints if their future will be here on earth?”
This verse is not alone in promising heavenly rewards to kingdom saints (Matt. 6:20; 19:21; Heb. 10:34). But Peter wrote to them about “an inheritance… reserved in heaven for you” (1 Pet. 1:4). Jews would understand from this that he wasn’t saying they would go to heaven to receive their inheritance. They would have known he meant that their inheritance would come to them on earth in the kingdom. The Lord told a parable in which…
“A certain nobleman went into a far country to receive for Himself a kingdom, and to return…And…when He was returned, having received the kingdom…” (Luke 19:12,15).
The nobleman represents the Lord (cf. Mark 13:34). The “far country” to which He traveled after His resurrection was Heaven. When He returns for Israel, He will return “having received the kingdom” that He will establish on earth for them. But in the meantime, all of the “treasures” of the Jewish kingdom saints are “reserved” there in Heaven with Him. source