He shall make him ruler over ( καταστη ìσει ἐπι Ì, with dative, denoting permanency of occupation; in Matthew 24:45 it is with genitive, as of temporary superintendence) all his goods; all that he hath.
This is the reward. He who before was set over only a small part of his lord's possessions is now made superintendent of all his property; for "he that is faithful in that which is least is faithful also in much" (Luke 16:10).
How we are to take this promise as applied to the rewards of the kingdom of heaven, we know not yet. "Eve hath not seen, nor ear heard, neither hath it entered into the heart of man to conceive, what God hath prepared for them that love him" (1 Corinthians 2:9).
There are similar mysterious statements elsewhere; e.g. Matthew 19:28; Romans 8:32; Revelation 2:26; Revelation 3:21. This may be one of those passages in which we are not meant to press or understand all the details of the parable.