Peter’s thought is derived from the truth expressed in Ps. 90:4. God is eternal. With Him there is no past, no future; all things are eternally present. He has no need for our limited concept of time, and we cannot confine Him or His ideas to our scale of days and years. In stressing this truth Peter is rebuking the skeptical impatience of the scoffers, who, judging God by their own puny standards, doubt whether He will fulfill His promises connected with the end of the world.
The context makes clear that Peter is not here setting up a prophetic yardstick for computing time periods. Verse 7 deals with the fact that God is patiently awaiting the day of judgment, and v. 9 that He is “long-suffering to us-ward.”
But.
The opening clause may be translated, “but let not this one thing escape your notice, beloved” (cf. v. 5). In other words, scoffers deliberately shut their eyes to facts, but Christians should never fall into that grievous error. “This one thing” is defined in the following clause.