The original purpose of belief systems (aka religions) can generally be defined as a system of thoughts, beliefs, values, principles that end personnel mental suffering or uncertainty through providing a life plan, knowledge list, behavior directions, priories, clarifications or how to live and treat others. Ethics, morality, decision making methods are often included. A system to end mental suffering is how Buddha defined his purpose. He went on to define the cause of suffering: expectations, delusions, attachment, aversions and provide a list of eight areas to examine and correct in our lives. Stoicism provided the correct way of thinking, a complete operating system to upgrade to. Epicureanism went further and suggested areas to eliminate that often create issues.
So the question is "how much of each system should the modern human adopt" to make life run better?
Some portion of relief of suffering is confidence that we are right. Doubt goes away. We can achieve this confidence by being part of a group that believes "x, y, z" or we can come to know that we are right through science, examination, testing, and/or association with like minded individuals. We can go against the flow of others as individualists only if we have the knowledge and confidence we are truly right.
All these three named thought systems place knowledge in their priorities. But the thoughts are not the same, but similar. With all the translation to get to English, along with the inexactness of language, how can we say that the original concept is not the same, but with the order and emphasis just different?
Much of Epicureanism just falls away as our science today is 2000 year ahead of what Epicurus knew and surmised. Yet stay out of things that will call us unneeded stress and worry is still good advice. Keep your oars where they belongs. Do not overreach. Do not overextend yourself too much, over
extension will cause stress. And minimization of our needs and intakes is sound finical advice. If we can do it is a totally different issue. Stay out of slippery places if we have fear of slipping. Stay sober, even when we drink.
Secular Buddhism cleans out the unreal items of reincarnation, and leaves karma as what it really is, reputation. Reputation is critical in long term relationships, especially is business. Yet we change over time, and some of us do not retain relationships well. Impermanence, the flipside of constant change is without a doubt just a derivative of change, aka the rate of change and whether we are able to see the change.
Danial Dennett has described the modern 'no self' reality, where consciousness is the mind observing the input/output flow but not yet understanding how the processing is done. Competence without comprehension. It is all knowledge we each can pick up if we put the effort, concentration and mindfulness in and just do it in our speech, actions and livelihood. Our intentions and attitudes provides the motivations.
One cannot separate the consciousness state from the objects of that state, as said Husserl, it is all in our heads anyway. Truth is the fundamental issue, and the non existence of a physical god is an essential and foundation fact. Until we can accept that, the truth is kind of nebulous, like ownership of a feral cat. Yet we can, in the mind of the believer have a god, the object of the mind, and live withing that god conscious state, not in full truth, but in full delusion. Many people will do all they can to keep living in that pink delusion where there is a god. It is the job of ever atheist to prick there mental balloon, or at least the balloons of the young. In the end we all just die off anyway, so if we can keep the young living in reality, we will do good.