St. Peter was not wrong when he declared at Pentecost that the last days had begun (ActsΒ 2:16,17). They had indeed begun, but God had a secret plan to give the world a period of grace before putting down its rebellion and sending Christ to reign.
This secret purpose concerning βthe dispensation of the grace of Godβ is the subject of Paulβs epistles. However, it is interesting to see how Peterβs last message explains the reason for this interruption in Godβs prophesied program and the delay in Christβs return to reign. First, he says in II Peter 3:8:
βBut, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years years as one day.β
Mark well, this is not our feeble explanation now as to the delay in Christβs return. This statement was made at the beginning of this time of waiting, at the dawn of the age of grace. But let us go on with Peterβs declaration:
βThe Lord is not slack concerning His promiseβ¦ but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentanceβ (II Peter 3:9).
So the delay in Christβs return to judge and reign should not be counted βslacknessβ or laxness, but longsuffering. Thus the Apostle goes on to say:
βAnd account that the longsuffering of our Lord is salvationβ¦β
Where did Peter get this information? How did he know about βthe dispensation of the grace of Godβ? II Peter 3:15 explains:
βEven as our beloved brother Paul also, according to the wisdom given unto him, hath written unto you.β
To Paul particularly was committed βthe gospel of the grace of Godβ which we proclaim today (ActsΒ 20:24). Peter recognized this (Gal. 2:2,7,9), and closed his second epistle with the exhortation:
βBut grow in grace, and in the knowledge of our Lord and Savior Jesus Christβ (II Pet.Β 3:18). source