God was not bound to forgive
It was not necessary for him to forgive; but if he does gratify his love in acts of pardon, he owes to himself, and to that everlasting difference between right and wrong which he himself has established, to do it in a way that satisfies and supports his immutable justice.
The necessity for the sacrifice of the Cross, therefore, is absolute. It is a necessity that is felt in all the stages of Christian experience; and where it is not felt, there is, there can be, no Christianity.
Unbelief in Christ as a Saviour is a necessary part of unbelief in God as a Judge. Men despise his mercy, because they do not respect his justice. One of the first lessons which the anxious sinner learns, is to feel his need of Christ. His conscience finds no relief, nor can it ever be disburdened of its mighty woes, save at the Cross.
The Attraction of the Cross, 48