St. Peter was not wrong when he declared at Pentecost that the last days had begun (Acts 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 “the dispensation of the grace of God” is the subject of Paul’s epistles. However, it is interesting to see how Peter’s last message explains the reason for this interruption in God’s prophesied program and the delay in Christ’s return to reign. First, he says in II Peter 3:8:
“But, 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.”
Mark well, this is not our feeble explanation now as to the delay in Christ’s 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 Peter’s declaration:
“The Lord is not slack concerning His promise… but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance” (II Peter 3:9).
So the delay in Christ’s return to judge and reign should not be counted “slackness” or laxness, but longsuffering. Thus the Apostle goes on to say:
“And account that the longsuffering of our Lord is salvation…”
Where did Peter get this information? How did he know about “the dispensation of the grace of God”? II Peter 3:15 explains:
“Even as our beloved brother Paul also, according to the wisdom given unto him, hath written unto you.”
To Paul particularly was committed “the gospel of the grace of God” which we proclaim today (Acts 20:24). Peter recognized this (Gal. 2:2,7,9), and closed his second epistle with the exhortation:
“But grow in grace, and in the knowledge of our Lord and Savior Jesus Christ” (II Pet. 3:18). source