His capacity was too small.
He voiced his doubt.
This Promise was too big for his faith to apprehend.
Making a Covenant was therefore God’s Way of expanding his faith.
He not only Promised but also Covenanted as to what He would do.
Thus did He cause him to Believe.
For having Established a Covenant, God could not help but Perform according to His Covenant.
Under the Security of such a Covenant, his capacity for Faith was naturally enlarged.