What the Old Testament might have left in doubt, the New Testament makes absolutely clear: when the Scriptures speak of the last days, they refer to the entire Christian age, from the first appearance and saving work of Christ to his Second Coming.
One of the earliest examples of this is found in Acts 2. Quick to answer the slur that the Spirit-filled apostles were full of new wine, Peter announced to his hearers that what they were witnessing was the fulfillment of the prophecy recorded in Joel 2:28-32. It is important to note that Peter clearly says that the words of the prophet were, at that time, being fulfilled "in the last days" (Acts 2:17).
In much the same way, 1 Peter 1:20 reports that Christ "was revealed in these last times." The passage places the recipients of the letter, the first-century readers, in "these last times." Peter lived in the last days.
By themselves, these two passages would make the case. But even more revealing is Hebrews 1:1-2:
In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom he made the universe.These first few words from Hebrews are especially important because they place Old Testament times and "these last days" side by side, identifying the second and concluding period as the time in which God has spoken to humanity by his Son. Because this was the common understanding and teaching in New Testament times, Paul could speak of Christians as those "on whom the ends of the ages have come" (1 Corinthians 10:11 NRSV).
What the Old Testament prophets saw as the future last days has become present reality through the work of God through Christ. According to the New Testament, the last days began with the ministry of Jesus and will conclude at his Second Coming. The biblical expression the last days refers to the entire Christian age, not merely to the very end of that age.
Without losing the edge of expectation, Christians must remember and teach that "no one knows about that day and hour, not even the angels in heaven, nor the Son, but only the Father" (Matthew 24:36). It is best to remain ready by consistently living as we should before God.