Mormon wants them to remember that they are the seed of Jacob so they belong to the first covenant which God made with Abraham. That covenant pointed toward the coming of Christ, so they should be baptized in the name of Jesus Christ and receive the Holy Ghost in order that all will be well with them at the great last judgment.
You have just read the last words Mormon will ever write. He was hunted down by the Lamanites and killed shortly after these words were written.