Jamieson, Fausset and Brown on Matthew 5:12

12. Rejoice, and be exceeding glad--"exult." In the corresponding passage of Luke (Lu 6:22, 23), where every indignity trying to flesh and blood is held forth as the probable lot of such as were faithful to Him, the word is even stronger than here: "leap," as if He would have their inward transport to overpower and absorb the sense of all these affronts and sufferings; nor will anything else do it.

for great is your reward in heaven: for so persecuted they the prophets which were before you:--that is, "You do but serve yourselves heirs to their character and sufferings, and the reward will be common."