Jude 1:24–25 (ESV)

24 Now to him who is able to keep you from stumbling and to present you blameless before the presence of his glory with great joy,

If you do not believe, then you are outside the favour of God. If you do not believe, the Scripture warns that you are condemned already. If you do not believe, the Scripture defines that you are—here and now—under the wrath of God. If you do not believe, there is reserved for you what Jude described as reserved for the unbelievers who were infecting the church—the blackness of darkness forever [Jude 1:13]. If you do not believe, there is remaining for you forever such an overthrow as the citizens of Sodom and Gomorrah experienced when the fire and brimstone fell upon them. A fire and brimstone which has burned them since that day until now, and will continue forever more. But if you do believe on the Lord Jesus Christ, understanding what he has done, that he might keep you from falling and present you faultless before the presence of his glory, if you do believe, then there is nothing in life but this: to God only wise, the honor and glory, dominion, majesty, praise, and worship. He alone is worthy.1

John McKnight