While a higher spirit may be able to visit a lower spiritual realm, the inhabitants of the lower realm are generally unable to see, or otherwise sense the higher order spirit. This is due to the increased vibrational state of the more advanced spirit. A good analogy would be the frequency range of the human eye. A typical human eye can see the wavelengths of visible light, from about 390 to 750 nm. Just because we cannot see frequencies above or below this range does not mean that they do not exist, and the majority of the electromagnetic spectrum is, indeed, invisible to our eyes.
Just as the human eye cannot see x-rays or radio waves, spiritual laws dictate that lower spirits cannot see spirits who vibrate in the higher spiritual frequencies until their own conscious states are raised enough to allow them to do so. This is one of the recurring themes in Dr. Wickland’s Thirty Years among the Dead (discussed in chapter 10).
The concept of spiritual frequencies also applies to living people as well. The reason that living people can see, hear and feel our earthly environment but cannot see or otherwise sense ghosts and any of the environments in the spiritual realms is because our frequencies and those of the material world vibrate in the same ranges. If your own physical frequency suddenly shifted to a higher or lower frequency range, you would lose contact with the material universe, and, of course everyone here would lose contact with you.
Everyone acquires a particular spiritual frequency which makes it possible for various spirits to affect us subconsciously. Lower personal frequencies facilitate contact with lower spirits who urge us subconsciously to commit bad deeds, while higher personal frequencies block these urges and facilitate contact with higher spirits who urge us to follow our better natures.
The frequency we attain during our lives varies from hour to hour and acquires a trajectory, like a stock market graph, over the course of our lives. The trajectory varies with the choices we make. There can always be major fluctuations on shorter timescales, but over the long run, if we live reasonably good lives with good intentions, the trend will generally remain on an upswing as we get older and wiser and learn to make better choices. Ultimately, the level of the frequency we acquire determines the spiritual level to which we “graduate” when we die and leave the material world behind. Don’t be worried! No matter what your trajectory has been in the past, it is never too late to make your stock rise! As maudlin or as out of date as it may seem, the character Ebenezer Scrooge in the novella “A Christmas Carol” by Charles Dickens is not a bad analogy