2-peter 3:8

Be not ignorant - Though they are wilfully ignorant, neglect not ye the means of instruction.

One day is with the Lord as a thousand years - That is: All time is as nothing before him, because in the presence as in the nature of God all is eternity; therefore nothing is long, nothing short, before him; no lapse of ages impairs his purposes, nor need he wait to find convenience to execute those purposes. And when the longest period of time has passed by, it is but as a moment or indivisible point in comparison of eternity. This thought is well expressed by Plutarch, Consol. ad Apoll.: "If we compare the time of life with eternity, we shall find no difference between long and short. Τα γαρ χιλια, και τα μυρια ετη, στιγμη τις εστιν αοριστος, μαλλον δε μοριον τι βραχυτατον στιγμης· for a thousand or ten thousand years are but a certain indefinite point, or rather the smallest part of a point." The words of the apostle seem to be a quotation from Psalm 90:4.

But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years - This 2 Peter 3:8-9 is the second consideration by which the apostle meets the objection of scoffers against the doctrine of the second coming of the Saviour. The objection was, that much time, and perhaps the time which had been supposed to be set for his coming, had passed away, and still all things remained as they were. The reply of the apostle is, that no argument could be drawn from this, for that which may seem to be a long time to us is a brief period with God. In the infinity of his own duration there is abundant time to accomplish his designs, and it can make no difference with him whether they are accomplished in one day or extended to one thousand years. Man has but a short time to live, and if he does not accomplish his purposes in a very brief period, he never will. But it is not so with God. He always lives; and we cannot therefore infer, because the execution of His purposes seems to be delayed, that they are abandoned. With Him who always lives it will be as easy to accomplish them at a far distant period as now. If it is His pleasure to accomplish them in a single day, He can do it; if He chooses that the execution shall be deferred to one thousand years, or that one thousand years shall be consumed in executing them, He has power to carry them onward through what seems, to us, to be so vast a duration. The wicked, therefore, cannot infer that they will escape because their punishment is delayed; nor should the righteous fear that the divine promises will fail because ages pass away before they are accomplished. The expression here used, that "one day is with the Lord as a thousand years, etc.," is common in the Rabbinical writings. See Wetstein in loc. A similar thought occurs in Psalm 90:4; "For a thousand years in thy sight are but as yesterday when it is past, and as a watch in the night."

3:8 But be not ye ignorant - Whatever they are. Of this one thing - Which casts much light on the point in hand. That one day is with the Lord as a thousand years, and a thousand years as one day - Moses had said, 90:4 , "A thousand years in thy sight are as one day;"which St. Peter applies with regard to the last day, so as to denote both his eternity, whereby he exceeds all measure of time in his essence and in his operation; his knowledge, to which all things past or to come are present every moment; his power, which needs no long delay, in order to bring its work to perfection; and his longsuffering, which excludes all impatience of expectation, and desire of making haste. One day is with the Lord as a thousand years - That is, in one day, in one moment he can do the work of a thousand years. Therefore he "is not slow:" he is always equally ready to fulfil his promise. And a thousand years are as one day - That is, no delay is long to God. A thousand years are as one day to the eternal God.Therefore "he is longsuffering:" he gives us space for repentance, without any inconvenience to himself. In a word, with God time passes neither slower nor swifter than is suitable to him and his economy; nor can there be any reason why it should be necessary for him either to delay or hasten the end of all things. How can we comprehend this? If we could comprehend it, St. Peter needed not to have added, with the Lord.