Hi there is only one place where the devil truly can be seen by humans and that is in the Bible with his start in the first seduction in the Garden of Eden where Eve and Adam were lured into rebellion, Genesis 3:1-5. Now first off Eve did not get the idea to eat of the forbidden fruit on her own, the idea was planted by a talking serpent. Why was "Satan" unseen? Was it to fool the woman? Was it to see how desperate she was or if she really believed in God?
There are many questions left unanswered concerning the devil as the tempter. But the way he started out still exists today, an unseen influencer that can surprise you at the results of his influence. Perfectly sane people suddenly have an incredible change within themselves and start behaving rebelliously for a definite reason. They will start a rebellious course that must be separated from honest hearted people. So actually, there is no real change in Satan's goal as the tempters since the original seduction into a sinful life, 2 Corinthians 2:11. We are awaiting the time called the Millennium because it removes the demonic influence for 1,000 years, Revelation 20:1-3. That is what the Bible promises us that has not happened yet because we are waiting for this influence to be completely removed.
