Yes he rewards us in secret so that we can't necessarily with proof "brag" about what God has done for us. It is to help us, not specifically give us bragging rights or being prideful of what we have or possibly done through God.
No, I spoke too soon. Most translations say that God himself is in secret:
American King James Version
But you, when you pray, enter into your closet, and when you have shut your door, pray to your Father which is in secret; and your Father which sees in secret shall reward you openly.
American Standard Version
But thou, when thou prayest, enter into thine inner chamber, and having shut thy door, pray to thy Father who is in secret, and thy Father who seeth in secret shall recompense thee.
Berean Literal Bible
But you when you pray, enter into your inner room, and having shut your door, pray to your Father, the One in secret. And your Father, the One seeing in secret, will reward you.
Holman Christian Standard Bible
But when you pray, go into your private room, shut your door, and pray to your Father who is in secret. And your Father who sees in secret will reward you.
International Standard Version
But whenever you pray, go into your room, close the door, and pray to your Father who is hidden. And your Father who sees from the hidden place will reward you.
NET Bible
But whenever you pray, go into your room, close the door, and pray to your Father in secret. And your Father, who sees in secret, will reward you.
New Heart English Bible
But you, when you pray, enter into your inner chamber, and having shut your door, pray to your Father who is in secret, and your Father who sees in secret will reward you.
Aramaic Bible in Plain English
But you, when you pray, enter into your closet and lock your door, and pray to your father who is in secret, and your Father who sees in secret will reward you in public.
King James 2000 Bible
But you, when you pray, enter into your room, and when you have shut your door, pray to your Father who is in secret; and your Father who sees in secret shall reward you openly