In this verse, Nephi reports a prophecy given by an angel that the God of Israel (meaning Jesus Christ) would come in 600 years from the time that Lehi left Jerusalem. Some revelations in the Doctrine and Covenants refer to timing of Christ’s mortal ministry as the "meridian of time" (D&C 20:26; 39:3). He came approximately after 4,000 years of recorded history, and there has been a little more than 2,000 years since then. The scriptures say that Jesus will come a second time in the beginning of the 7th thousand years. We have finished 6 thousand, and so we are now in the beginning of the 7th thousand years. We do not know exactly when the Second Coming is, but it is getting closer.
There is a time set, and He is going to come when He is supposed to come. It is our duty to be ready and to watch for the signs. Some people say "the Lord delayeth his coming" (Matthew 24:8), but He is not delaying His coming, and we cannot make Him come faster just because of what we do. He is going to come when it is time for Him to come. So, we should watch and be ready because that is what He told us to do, to look for the signs and be ready for His Second Coming.
Do we know that he is coming again? Yes. Just as much as Nephi knew that he was coming the first time. Nephi was a great prophet. He believed in Christ, that he would come in 600 years after they left Jerusalem. We believe that Christ is coming again, maybe during this century. I do not know when, but it is getting closer. He is going to come in a day of wickedness. He is going to come in a day of wars and rumors of wars. That is happening. Earthquakes in diverse places—there are all kinds of signs of the times that are happening. In fact, if you just make a list of all the signs of the times, most of them have already happened because many of the signs had to do with the restoration of the gospel, including the coming forth of the Book of Mormon, the establishment of Jesus Christ’s Church, the missionary program taking the gospel to the world, and the gathering of Israel. If you make a list, most of the things that need to happen before he comes have happened.
There is one verse in Matthew 24 that is my favorite verse pertaining to the timing of Christ’s return. Jesus said: "And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come" (Matthew 24:14). So just watch the missionary program and watch for this gospel to be preached in all the world, and it is probably going to happen in some ways that we are not expecting. When I was a bishop at Brigham Young University, I gave a fireside in 1988 and said to the BYU students in my ward, "You will see the day when missionaries go to Russia and behind the iron curtain, and you will see the day when we have churches and temples and stakes of Zion in what is now the Soviet Union." And just a short time after that President Reagan said, "Mr. Gorbachev, tear down this wall!" Not because he said it, but because of what happened, the wall came down and the Soviet Union collapsed and missionaries of The Church of Jesus Christ of Latter-day Saints went into all those countries.
Book of Mormon Central, "How Does Prophecy Shape the Book of Mormon’s Content and Structure? (Words of Mormon 1:4)," KnoWhy 498 (January 15, 2019).