Answer:
We must realize that what Christ did on the cross for our sins was provisional in nature. Being provisional, there is therefore the need to receive and avail ourselves of it through faith in Him and what He did on the cross, if we are to enter into the good of it.
Yes, the Lord Jesus Christ provided the payment for our sins when He died on the cross, with God giving His nod of approval of it when He raised Him from the dead.
But that provisional atonement/payment can only be applied actually to us and to our sins the very moment we receive it by faith in Him.
If we learn to distinguish between provision and application, then double payment is not an issue. Since the provision is never applied automatically to all but is only applied to those who trust in Him.
His death on the cross was sufficient for all the world, but it is applied only to those who put their trust in Him.
Joh 3:16 "For God so loved the world that He gave His only begotten Son, that whoever believes/trusts in Him should not perish but have everlasting life.
1Ti 4:10 For to this end we both labor and suffer reproach, because we trust in the living God, who is the Savior of all men, especially of those who believe.
