When God created the world, He knew that we, the vessels, could not receive His awesome, blazing Light in Its totality. This Kabbalistic notion can be likened to a tripped circuit breaker caused by an overload of electric current. It can also be compared to the light of the sun, which would incinerate the entire earth if it were to ever approach too close. The Creator, in His infinite wisdom, therefore concealed the greater portion of His Light so as not to overwhelm that which He created. The Zohar recounts the process of how this hidden Light began to be revealed.
As we correct and transform our crude, immoral nature, we reveal a measure of hidden Light in direct proportion to the degree of inner change we've undergone. It is this spiritual change that expands our internal vessel, allowing us to receive a greater portion of hidden Light. The Hebrew letters radiate this hidden Light into our day-to-day existence.