Ques. Why did God command, "Be fruitful and multiply and replenish the earth," if all minds (men) have existed from the beginning, and have had successive stages (or dreams) of existence to the present time?"
Your question implies that Spirit, which first created the universe and man spiritually, created these over again materially, and by the aid of man all was made which He had made. If the first record is true, what evidence have you, apart from the evidence of that which you admit cannot discern spiritual things, of any other creation? The creative "Us" had made all. Mind was the Creator, hence man originated not from earth nor materially, but from Spirit and spiritually. This work had been done; the true creation was finished, and its spiritual science stated.
Jesus said of error, "What thou doest, do quickly." By the law of opposites, after the Truth of man had been demonstrated, the postulate of error must appear. That this addenda was untrue, is seen when Truth, God, denounced it, and said: "I will greatly multiply thy sorrow. In the day thou eatest thereof, thou shalt surely die." A lie saith, I am true. This error said, "The Lord knows that thine eyes shall be opened, and ye shall be as Gods, creators." This was false; the Lord had never said it. This is the history of a falsity; but a lie must be told in the name of Truth, or it would not be a lie.