The verb might reign is subjunctive and indicates that grace might not reign. Let us therefore come boldly unto the throne of grace, that we may obtain mercy , and find grace to help in time of need. Now faith is the substance of things hoped for, the evidence of things not seen. Faith is the substance that allows us to please God. Only the just, obedient, can live by faith.
Faith gives substance to grace.
If we do not access grace by faith we will not have the power of God we need to endure. There is a time when the verb believe and the noun faith are the same, and that is when the verb believe is used as a present active participle. A participle can be an adjective or a noun. When the participle has the definite article the before it, the participle is used as a noun. The following three verses are the only verses that have both the present active participle of the verb believe with the article and the noun faith .