Why was Simon's belief not genuine?
Simon’s belief was not genuine because he believed only with his head, not with his heart. His motive was seeing material gain, so his faith was intellectual and self-interested rather than wholehearted. Scripture requires belief with the whole being, the innermost heart.
Les explains that Simon, up in Samaria, did believe, but not with his heart. His belief was only head knowledge because he could see material gain. By contrast, Philip tells the eunuch that belief must be with all the heart. Les points to Romans 10 and says Scripture requires belief with our whole being, our innermost being, the heart. This has always been the standard, as with Cain and Abel: Cain brought something, but he did not do what God said, so he was without faith, and without faith it is impossible to please God. The Ethiopian eunuch, having heard what God required for salvation, believed it with all his heart.
More Questions
Why did Simon's belief in Samaria not count as real faith?
Simon in Samaria was an example of head-belief only, because he believed for the material gain he saw rather than with his heart.