Nature is all that exists.
Everything that exists is part of Nature.
Nothing exists outside of Nature.
The past, present, and future are part of nature.
Humans are part of nature. Our minds, consciousness, and imagination are part of nature. However, we are capable of imagining things that do not exist, and frequently do so. Things that we imagine that do not actually exist in nature have no existence; only our thoughts of them exist.
Nature is very complicated. The human brain evolved to help us survive within nature; its ability to understand nature is by no means perfect.
We may not know the full extent of nature. A few centuries ago humans thought Nature was limited to our solar system. Now we know that nature is vast, including, at the least, our own galaxy and the many galaxies visible through telescopes. There are many particulars of nature we are not aware of yet.
Since Nature is real, it can neither be created from, nor destroyed by, human thought. Human thought is subordinate to nature.
Human awareness is caught up in time. We are always in present time. But the past is real, and the future is real or is becoming real. We know of the past from our memories and from examining its artifacts.
It follows that since the past is real, events of the past are real, and those who lived in the past were and are real. While it may be sad for us when our friends and relatives die, it should comfort us that their lives were real. There is no need to postulate a heaven to reward the good or a hell to punish the evil. Life is its own reward. Let those who are alive and deserve punishment be punished: nothing needs to be done about the dead.
Religions, like other aspects of human culture, arise out of Nature, but they generally are mistaken about it. Religious beliefs sometimes arise out of legitimate mistakes that are misinterpretations of the complexities of natural reality. Some beliefs arise out of hope or from wishful thinking. But Religion is usually made concrete by men who find some advantage over their fellow men in it. Once instituted, religion can have a powerful effect on the human mind, since humans are apt to mistake words, especially words frequently repeated, for reality.
The Evolution of Species over time by mutation and natural selection is the key truth to our understanding the biology of nature, and our own nature.
Conscious awareness arises out of nature in the context of the human nervous system combined with interaction with the natural world and with human culture. Humans may not be unique in being consciously self-aware.
Ethics arise out of human culture, which arises itself out of nature. Religions have made contributions, both positive and negative, to the development of human ethical systems. The key to correct ethical precepts lies in accepting ordinary human life as real. Life is not a test to get into heaven, or to score points for a better berth through reincarnation. When humans suffer, they suffer in reality; when they murder, the murders are real; when they harm, the harm is real; when they do good, the goodness is real.
The two most basic ethical rules are to treat everyone fairly and to favor truth over falsehood.