I am sure each image will vary according to each reader, but let me give you a basic explanation here.

I. The Treasure at the Bottom of the Sea
This is a symbol illustrating your capabilities and potential concealed within yourself. If you would drive this image into your heart, you would be able to understand the meaning the symbol carries for you suddenly one day, and/or it will appear before you in reality. As you go on observing the treasure carefully, it may begin to change, and give you a message.
But even if the treasure might not come out to appear, do not be disappointed. It just did not happen to come out this time, that's all. It will surely come out someday later. Or perhaps, it may be something that could be felt by the touch or the hands and not necessarily visual. Whichever way, please do not rush, and try many times as much as you like. In order to make the descent to the unconscious world, I presume time and repetition are necessary.
A guided imagery concerning this is in the attached CD to the previous book "The Time Machine of Healing", so please listen to it and practice training. I especially recommend it to someone who is suffering one's own loss of confidence.

II. The Lighthouse
A certain kind of symbol has the power to give a big change in one's life, or to state exaggeratingly, to even one's soul. Symbols are effective in changing the conditioning in one's self, and to find the direction of one's own new energy. The imaging in Chapter Six is especially effective for freeing oneself from a difficult situation one has fallen into, and to regain a sturdy sense of stability.