I have believed in the past that a Preterist interpretation of “last days” language in the New Testament was the most reasonable understanding of it, holding that the “last days” were the end of the Old Covenant. But it was something I had never given the time it deserved, and I don’t think my broader understanding of Scripture was sufficient to come to a conclusion on the matter. I’ve spent some time looking at 1 Peter recently, examining the Greek, comparing it with other passages that speak of “the end”, and taking in passages that speak of the bodily resurrection (1 Corinthians 15 and 1 Thessalonians 4). And I don’t believe the Preterist reading of that language is full enough to cover everything the New Testament means by it. It seems to me now that a more Biblically accurate reading to be made of this is to see the “last days” as referring to the final period of God’s eternal plan of salvation - that is, the whole scope of history stretching from the incarnation of Christ on into eternity. This includes the overlapping of the Old Covenant and the New Covenant that occurred in the the first century, but does not refer simply to the end of the Old Covenant. This still leaves place for a Partial Preterist understanding of the fulfillment of prophecy, including the Book of Revelation. A part of Christ’s work was that of bringing the Jewish system to an end, in fulfilling it by doing what it could not do and by bringing in the Gentiles so that, with Jewish believers, all the nations of the earth might worship Him as His Church. This also includes a positive, Postmillennial view of history - Jesus is victorious, and will continue to be so, through His Church, until all people bow to Him. Peter’s letters are filled with this positivity, emphasizing it as a reality to be seen even in the midst of suffering.
A full consideration of this would take more than I’ll attempt right now. After all, pages upon pages have been written about it throughout history. Whether I will try to cover some of my reasoning in the future only time will tell.
But, I will note, the Lord tells us that “the God of peace will soon crush Satan under your feet” ( Rom. 16:20), and “soon” is according to God’s perfect judgment, not our own limited view. “Jesus Christ...has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him” (1 Peter 3:21-22). He is “seated...in heavenly places, far above all rule and authority and power and dominion, and above every name that is named“ (Eph. 1:20-21). And He is currently “destroying every rule and every authority and power” (1 Cor. 15:24), even through us, as we “tear down strongholds” (2 Cor. 10:4) by the example of our lives and as we “make a defense to anyone who asks (us) for a reason for the hope that is in” us (1 Peter 3:15).
“To him belong glory and dominion forever and ever. Amen” (1 Peter 4:11). Jesus is King, and He reigns now over all things from His throne in Heaven. And He will do so until “the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power. For he must reign until he has put all his enemies under his feet”(1 Cor. 15:24-25), when finally God will “be all in all” (1 Cor. 15:28).