Muso Kokushi has a no-frills, straight forward approach to explaining zen and it's practical uses.
Here are a couple quotes I liked
Aim in Life
There is ultimately no means of safeguarding anything in this world; anything you gain can be lost, destroyed, or taken away. For this reason, if you make the acquisition and retention of goods or status your aim in life, this is a way to anxiety and sorrow.
Past, Present, and Future
It is a characteristic tendency of human beings to indulge in emotions such as happiness, grief, or anger in response to present conditions, failing to balance these feelings with the awareness that present conditions are results of past causes. It is illogical to face the present only as an object of enjoyment or tolerance, neglecting to use it as the opportunity to create the future.
The Inexhaustible Treasury of Potential
There is a vast potential, latent within human beings, that remains undiscovered because of the limitations placed on consciousness by habitual preoccupations. The recommendation that all cravings be relinquished does not mean that detachment itself is a goal; it is a means of breaking through self-imposed restrictions and opening up this inexhaustible treasury of potential.
The Central Benefit of Zen
The central benefit of Zen, in the context of the ordinary ups and downs of life, is not in preventing the minus and promoting the plus but in directing people to the fundamental reality that is not under the sway of ups and downs.