We can assign a purpose to life but after we do we can still ask "Why?" If we do ask it we will find we can not know in the usual sense the answer to this last "Why?"; and that missing fact is the void in our lives. That aside, all the biological evidence suggests the purpose of life is self-realization. Becoming what we are capable of being is the consequence of what I call natural activity. I define natural activity as reaching out to the limits of our physical/mental capacities to others and to God. It is innate activity that unquestionably begins at conception.
Although innate, natural activity is one of two possible types of activity we can choose, because natural activity is not mandated by "the law of human nature". The "law" allows us, when we have the necessary realized mental capacity, to ignore our innate purpose and replace any measure of natural activity with an equivalent measure of unnatural activity. I define two types, trying to fill the void and giving up. However, substituting increasing amounts of either unnatural activity for natural activity results in correspondingly greater self-destruction and life diminished accordingly, eventually to the point of unnatural death.
Even though it is one of the two complementary possibilities of life, it must be obvious that self-destruction can not be the purpose of life. In self-destruction and death there is absolutely no hope of ever knowing the reason for self-realization. In self-realization there is at least the hope that we might discover the reason for life; and thus there is purpose in reaching out the limits of our capacities, to others and to God. see (the last why: the poem or the precis or the essay)