What does this quote from the Lotus Sutra mean?

I suggest caution when analyzing quotes like this before seeing nirvana for the first time. It is extremely easy to be misled and fall into a "trap" when you hear any quote that says something along the lines of "you already possess all that you seek." If you have not awakened yet, do not read my interpretation of the quote as a call for you to stop your practice or stop seeking the truth. That being said, this is my interpretation.

You, the richest person in the world,

The first time "You" is being used in this sentence, it is referring to the illusory self. The human being we all believe we are when we first begin experiencing this world. This you is referring to a small part of your experience, the concept that you currently identify as what makes up your identity.

have been laboring and struggling endlessly,

This is referring to the struggle of Samara. Laboring is referring to the endless cycle of wanting something putting in effort to try to obtain it. Struggling is referring to the difficulties we encounter, as well as the suffering we feel when we do not get the things we want.

not understanding that you

Now this part of the sentence is where things get confusing, because the speaker is no longer using the word "you" to refer to the illusory self. The speaker has now (in a very confusing way in an attempt to be poetic) switched the meaning of the word "you" to refer to the inexplicable. Although it is incorrect for me to say, the clearest explanation I can give of the "you" that is being referred to in this context is the "you" that is "one with everything". Understanding that, things become a little more clear.

already possess all that you seek.

To fully explain this, a small explanation of desire and the process of forgetting is needed. This all comes from my personal experience, so take what I say with the normal amount of skepticism. Don't believe what I say, for unverified statements are what keep us trapped in the cycle of Samsara. Verify what I say in your own experience. It is through observing my own experience without belief that I was able to be whole.

It is impossible for one not to be themselves. I have been my true self forever and always, but there was a time where I forgot who I was. When one believes they are a human being, they are blinded by that belief. What happens is, a being who is infinite and eternal, suddenly believes that it is small and mortal. This process of forgetting can be said to be a process of exclusion. At first you are everything. Then, we begin to say, "I am not this, I am not that," etc. until we have come to the conclusion that we are not most things, but are something very small and insignificant in comparison to the universe. We know, deep in the core of our being, that we are not meant to be small and mortal. This instinct, the feeling of lack that permeates our experience, is what gives rise to desire. We only desire what we lack. We think, "I am not this, in order to be whole, I must attain this. Once I get this I will be fulfilled." But because we are everything, and it is impossible for a human being to attain everything in their lifetime, we are stuck in the endless cycle of Samsara.

So to quickly summarize: We only desire because we feel like something is missing. We feel like something is missing because we believe we are a limited number of things. We feel like we are a limited number of things because we have forgotten what we truly are, which is "one with everything".

Now, to finally explain the last part of the sentence: It is not saying "you the human being already possess everything you need in your life." It is saying that "you", the ultimate you, are everything that you seek. The speaker is talking past the illusory self, the human, and saying "You, the real you that is there, you are everything in the universe. Everything this human desires, is simply a part of your identity. The human does not understand that it, and the object of its desire, are both you."

It is attempting to describe the amazing plight of being human. It is like a wave in the ocean, chasing another wave. The wave says, I need to reach the other wave! I want to merge with that wave and become an even bigger wave, and then I will be whole! When the irony of the situation is, the wave is already the entire ocean.

I hope my words have been helpful to you in some way. I pray for nothing more than your liberation this lifetime.