Any purpose that we have will have to be self-created; nobody can do that for us. That purpose will not be appreciated by ourselves after our deaths but it may be by those follow us. This may be the closest that we get to immortality.
In general, humans inherit genes from parents which are a random pick from a number of possibilities which can be beneficial or detrimental to passing on a set of genes to the next generation before death. The genes that are most beneficial to passing them on will tend to be the ones that survive more often. If it were not for this process of birth and death we would not be here.
In this sense, our death is the cost that we pay for having a chance to live.
