In the LDS Gospel, we believe that we lived before this life, as spirits, literal creations of Heavenly Parents. We also believe that we will have a life after this one, where eventually we will be reunited with a perfected form of the body we have in this life, to continue to progress to being like out Heavenly Mother and Father. We understand two very specific reasons for this mortality, and have quite a bit of speculation on other reasons for mortality.
First, we needed to have a body. Our Heavenly Parents had physical forms, but we did not. To become more like them, we needed to also have physical forms added to us, though these physical forms weren’t without down sides. The instincts, the nature of these bodies would have both good and bad qualities, which would need to be tempered and brought into submission with the laws set up God (our heavenly Parents). Giving in to some of these instincts would be a form of sin, with which we could not be in the presence of our God. To compensate for the inevitable sin by every child of God, a Savior was needed, and provided, in the meridian of time.
Second, there are ordinances that need to be accomplished to both affirm the desire to follow God and endow us with some of the Power of God if we follow His (and Her) will. This is Baptism and the other ordinances LDS go through for themselves and their dead in the Temple. Baptism is not simply for cleansing us from sin, but also to show our commitment to follow God’s will. This is why Jesus also submitted to Baptism, even though He was sinless. This is why the work to Baptise the dead (by proxy) is necessary for all those who have attained an age where they could make that commitment. We don’t simply wait for the dead to be resurrected to be baptized, because evidently this work needs to be done by someone who is mortal. (I don’t know why, but that is the only reason I can see for doing proxy work at all)
Now, to the speculations. I’d submit one – the need to experience pain. Everyone, no matter how long they live on this Earth, experiences some pain. It may be brief, but every one who has lived has experienced both physical and spiritual pain. Those who have lived the briefest of lives have not only felt the physical pain of their journey to death, but also the spiritual pain of being separated from the mortal parents they were born to.
Some have postulated on the necessities of childbearing, parenthood, marriage, and many other things seemingly necessary to fully experiencing mortality, but all these are extras. They may be enjoyable, growth inducing extras, but they are extras all the same. Why some of us need these extras is known to our Heavenly Parents, and we have to trust in their wisdom and timing. I put these all into extras because all of these do not happen for many of God’s children. Those of us in mortality do have growth and learning to do in this life, and we should not speculate on why some of us are given some experiences that others are not, but we can trust that the learning and experience we have in this life are intended for our growth, no matter if they are hard, joyful, scarring, or easy.
What is the point of mortality? In general, we can only come up with a few points. Individually, we can scarcely speculate, since we have no perspective or even knowledge of each individual in the eternities. We can only do the best we can with what we have been given, and do our best to help others on their way.