Institutes of the Christian Religion (1559) - John Calvin
Book 2 - God the Redeemer
Chapter 11 - The Difference between the Two Testaments
Sections 13-14 - Reply to objections regarding God's justice and consistency in these differences of administration
Section 13 -Why, in general, the differences?
Parents aren't inconsistent because they parent differently according to the age of the child. Neither is God in dealing with us.
Rather, He "accommodated Himself to men's capacity, which is varied and changeable."
Section 14 - God's freedom to deal with all men as He wills
"God has done everything wisely and justly."
It is up to Him if, where and when to reveal His salvation.
He may "deprive the world, because of its ungratefulness, of the knowledge of his name for such ages as He wills."