What is the 'reward' that Jesus is referring to in Matthew 6:6?

> But when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you. - Matthew 6:6 NIV I would like to think that 'reward' refers to answered prayers. But 'true' believers of Christ should ***know*** that God answers prayer (James 5:16), so it seems unlikely it is referring to just that. What is an overview of different interpretations of what 'reward' in this verse is referring to.