Ahhhhh my friend, I must tell you that you are SO wrong here. Of course we know it. It isn't just that the Bible tells us that we are spiritual beings first and foremost (and of course, I believe the Bible unswervingly), but there have been countless thousands of NDE's documented over many years. I've read several books on the topic; the experiences bear striking similarities no matter the person's race, age, ethnic background, country of origin, etc.
Yes, there is definitely life after death, and it is incumbent upon us to follow God's law but not "just in case"; we do it because our spirit beings long to be with Him and long to commune with Him. Those who either ignore this or claim not to know it seek that fulfillment in many destructive ways, never seeming to realize what they are really missing in this life. This life, the next.....inextricably intertwined.
Yes, I heard of NDE experiences where a single person watched the goings on and described them accurately to the surprise of medical personal, et al.
I made a statement of fact that if there is no life / consciousness / awareness / whatever after death then we will never know it. Period.