You say one of the common messages in all these religions was what we now call the Golden Rule. And Confucius was probably the first person who came up with this idea.
All these sages, with the exception of the Greeks, posited a counter-ideology to the violence of their time. The safest way to get rid of egotism was by means of compassion. The first person to promulgate the Golden Rule, which was the bedrock of this empathic spirituality, was Confucius 500 years before Christ. His disciples asked him, "What is the single thread that runs through all your teaching and pulls it all together?" And Confucius said, "Look into your own heart. Discover what it is that gives you pain. And then refuse to inflict that pain on anybody else." His disciples also asked, "Master, which one of your teachings can we put into practice every day?" And Confucius said, "Do not do to others as you would not have them do to you." The Buddha had his version of the Golden Rule. Jesus taught it much later. And Rabbi Hillel, the older contemporary of Jesus, said the Golden Rule was the essence of Judaism.
What is religion?
Religion is a search for transcendence. But transcendence isn't necessarily sited in an external god, which can be a very unspiritual, unreligious concept. The sages were all extremely concerned with transcendence, with going beyond the self and discovering a realm, a reality, that could not be defined in words. Buddhists talk about Nirvana in very much the same terms as monotheists describe God.
In my book "A History of God," I pointed out that the most eminent Jewish, Christian and Muslim theologians all said you couldn't think about God as a simple personality, an external being. It was better to say that God did not exist because our notion of existence was far too limited to apply to God.
Jesus did not spend a great deal of time discoursing about the trinity or original sin or the incarnation, which have preoccupied later Christians. He went around doing good and being compassionate.
very often, the opinions of the deity are made to coincide exactly with those of the speaker
People such as the Buddha thought miracles were rather vulgar -- you know, displays of power and ego. If you look at the healing miracles attributed to Jesus, they generally had some kind of symbolic aspect about healing the soul rather than showing off a supernatural power.
Western people think the supernatural is the essence of religion, but that's rather like the idea of an external god. That's a minority view worldwide.
Is faith a struggle?
Well, faith is not a matter of believing things. That's again a modern Western notion. It's only been current since the 18th century. Believing things is neither here nor there, despite what some religious people say and what some secularists say. That is a very eccentric religious position, current really only in the Western Christian world. You don't have it much in Judaism, for example.
People can perform their good deeds in the spirit of putting their installments in their retirement annuities. And there's nothing religious about that. Religion is supposed to be about the loss of the ego, not about its eternal survival.