One thing that we do know about the Tractatus is that in it propositions with more numbers are supposed to be clarifications, (or perhaps reactions) of the propositions that have less numbers (so all propositions are clarifications to the 7 main propositions). In particular proposition 6.4311 is a clarification of 6.431. There are just two propositions that follow 6.431, so I will quote the whole passage here, along with 6.43:
6.43 If the good or bad exercise of the will does alter the world, it can alter only the limits of the world, not the facts--not what can be expressed by means of language. In short the effect must be that it becomes an altogether different world. It must, so to speak, wax and wane as a whole. The world of the happy man is a different one from that of the unhappy man.
6.431 So too at death the world does not alter, but comes to an end.
6.4311 Death is not an event in life: we do not live to experience death. If we take eternity to mean not infinite temporal duration but timelessness, then eternal life belongs to those who live in the present. Our life has no end in just the way in which our visual field as no limits.
6.4312 Not only is there no guarantee of the temporal immortality of the human soul, that is to say of its eternal survival after death; but, in any case, this assumption completely fails to accomplish the purpose for which it has always been intended. Or is some riddle solved by my surviving for ever? Is not this eternal life itself as much of a riddle as our present life? The solution of the riddle of life in space and time lies outside space and time. (It is certainly not the solution of any problems of natural science that is required.)
So when reading 6.43, we can conclude with a reasonable level of certainty that the topic of the whole passage is the subjective aspect of reality. In it, Wittgenstein points out that although all of us are living in one and the same world, shaped by the same set of facts, each of us experiences reality in a completely different way. He even gives what is probably the only example in the whole book by saying: "The world of the happy man is a different one from that of the unhappy.
Passage 6.431 says that if the our perception of the world is subjective, then when we die, our whole world dies with us. So there isn't a point in time where our world exist without us in it.
Passages 6.4311 and 6.4312 set forth the idea that it does not make sense to compare our world, our lifetime with anything else. So it does not make a difference how many times does the Sun revolves around the Earth while we are alive i.e. how many years do we live - no matter if they are 10, 100 or 1000, our life is equally infinite (although it does not encompass the whole of reality). In the same way, our field of vision is infinite although we don't see the whole world. This is contrasted by the usual common-sense notion that living longer and in leaving some kind of mark brings you closer to immortality and even might help you reach it.
Seems like this idea might be inspired by the Kantian notion of subjective space and time (Wittgenstein mentions Kant a couple of paragraphs later for unrelated reasons). And the conclusion is also similar to that of Kant's - science and spirituality are very different things, so it does not make sense to compare them with one another.
