JOEL - Your speaker in Sacrament meeting may have been expressing their own opinion on the matter, because as I have said in other responses there really is no official opinion from the church leaders as to when the spirit enters the body. There are basically three periods when a fetus could acquire its spirit: 1) at conception, 2) at 'quickening' (the first movements of life felt by the mother, usually in the fourth month of pregnancy), or 3) at birth. Interestingly, each of these three periods has had its supporters among the leaders of the Church.
According to James E. Faust:
"Some say, as did the Supreme Court of the United States, that it is only theory that human life begins at conception. This is contrary to insurmountable medical evidence…Because she feels it, every mother knows there is sacred life in the body of her unborn babe. There is also life in the spirit, and some time before birth the body and spirit are united. When they do come together, we have a human soul. (Ensign 5:27-29, May 1975)."
Exactly when it happens is something that God has not revealed to us yet.
You ask "how can anything be alive and not have a spirit?" As a scientist I have often worked with tissue cultures where we grow human skin cells for example in a test tube. These are human cells I am growing but they are not nor ever will be human beings. Yet they are considered living cells because they are growing and multiplying, as long as I provide the proper nutrients and environment. I am quite certain that these living cells have no spirit. This is how something can be alive and not have a spirit (IMHO). The big question is, can this same logic be applied to a living growing embryo that has the potential to become a live human being? At what point does this mass of cells, become more than just living cells?
According to Elder Russell M. Nelson:
"It is not a question of when “meaningful life” begins or when the spirit “quickens” the body. In the biological sciences, it is known that life begins when two germ cells unite to become one cell, bringing together twenty-three chromosomes from both the father and from the mother. These chromosomes contain thousands of genes. In a marvelous process involving a combination of genetic coding by which all the basic human characteristics of the unborn person are established, a new DNA complex is formed. A continuum of growth results in a new human being. The onset of life is not a debatable issue, but a fact of science." (Ensign, May 1985, 11)
Therefore, an embryo is a new separate living human being from the moment of conception, and for this reason alone we should never consider commiting the sin of abortion; but that still does not answer the question of when it becomes a complete soul, with both body and spirit. I am afraid that there are no answers yet to many of your questions. And since we do not know when the spirit unites with the body we must oppose such things as abortion or partial-birth abortions, because we cannot be certain that we are not ending the life of not only a living being but a complete human soul.
President Spencer W. Kimball taught: “There is such a close relationship between the taking of a life and the taking of an embryonic child, between murder and abortion, that we would hope that mortal men would not presume to take the frightening responsibility. . . .(Teachings of Spencer W. Kimball, Salt Lake City, Utah: 1982, p. 188.)
Of course God will never punish the baby,(ie. cause them to be stuck in the premortal side) because someone else decided to end the life of its body. In the case of abortion, if the spirit was already in the body the child will be assured of exaltation in the Celestial kingdom. If the spirit had not yet entered the body it may have the chance to enter another body. This of course assumes that the spirit does not enter at the moment of conception. This of course is my own opinion.