John MacArthur in his New King James study bible says on pg. 1423 in his notes on Matthew 16.19.
NKJV Matthew 16.19 And I will give you the keys of the kingdom of heaven, and whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven."
John says and I quote " When the church acknowledges that a repentant person has been loosed from that sin, God agrees"
John here is investing in men(church) not God's ability to judge and forgive! Ouch!