Who is the Father who sees what is done in secret?
Matthew 6:6 (ESV)
6But when you pray, go into your room and shut the door and pray to your Father who is in secret. And your Father who sees in secret will reward you.
The Father is God. He fills all places with his presence and transcends all spatial limitations (1 Kings 8:27; Psalm 139:7–10; Isaiah 66:1; Jeremiah 23:23–24; Acts 7:48–49; Acts 17:27–28).1
6 But when you pray, go into your room and shut the door and pray to your Father who is in secret. And your Father who sees in secret will reward you.