we are the universe, and if we and the animals and the plants and all life have a purpose, to live and survive and prosper, then the universe has a purpose. and as life's consciousness we can tell what is good and bad, what is high quality and low quality, what is amazing and horrible, so we have both the senses and the tools (science) to take the universe in the direction we want. and perhaps this is happening without us being aware of it or accepting it or not. but even to reject it one would have to contradict himself, because every particle and atom of his mind is part of the universe which he rejects, so that the very act of rejection is part of that which is rejected. and the potential of the universe is endless and infinite. perhaps as an individual i am cut off from predicting what will happen when that complex being comes into existence, compared to whom i am like an amoeba. but what of it? i dont need this knowledge to know that the substance of which i am made is part of the life and conscious-joy of the universe, and that it seems to be moving in a certain direction, and my moving against it will not serve any purpose. yes, and perhaps i do not matter in the great scheme of things, and it doesnt really affect much of reality if i choose to do "evil" rather than "good," and vice versa, but this is beside the point! i am simply a small instance of that great movement that is the conscious part of the universe, and my decisions in life are my personal problem. as long as i and all other life are not disconnected from what we are made of, and not moving against it and slowing it down, my personal choices don't matter so much, and the universe will be fine. i suppose this gives us excuse to do "evil" because there is no personal punishment or accountability provided in most religions. but if we know what and who we are and where we must go, why would we do "evil"? it would be a self-contradiction and would not serve anything in existence. in religions we are given the "devil" to serve, but serving this is like a disease, a tumor in the brain, using its own cells to destroy itself.
and if i am asked, how do i know what and who i am and where i must go, and how do i know that my sense of "amazing" and "good" is not completely arbitrary and purposeless, the answer is i don't, but i am simply trusting my instinct, which is what you are doing when you ask the "how do you know" question in the first place, when you seek the truth, so that you can be sure of reality and not live in denial the way a religious person might. you are seeking the truth with science because you want to live and survive and prosper, because you care, because you think that living in denial is not amazing, in fact it is quite horrible.