Reading from Ceslaus Spicq, Agape in the New Testament:
But love ye your enemies, and do good, and lend, hoping for nothing again; and your reward shall be great, and ye shall be the children of the Highest: for he is kind unto the unthankful and to the evil. (Luke 6:35 KJV)
The joy of the persecuted (v.23) can be unconstrained even here on earth (rejoice at such moments).
The great reward of the charitable, who have so much to suffer in the present, is reserved for the future (your reward will be abundant).
Only the happiness of heaven can furnish a superabundant compensation.