Shikan Taza, or Just practice Zazen
Shikan means "solely, or just," and Taza means "practice Zazen!" Therefore the words Shikan Taza means "Just practice Zazen," and so it means that Zazen is just Action, but it is never a only verbal expression of Zazen. Zazen is just Action, which has been utilize as a practice to have our ANS balanced.
Therefore the practice of Zasen is just useful when it is just actually practiced, but it is perfectly useless for us to explain or discuss Zazen only verbally.
However, actually speaking, people usually like to speak or discuss Zazen verbally, but exactly speaking, people usually do not like to practice Zazen actually.
And so Master Dogen proclaimes that "Do practice Zazen actually." That is just the meaning of words "Shikan Taza."
Therefore the practice of Zasen is just useful when it is just actually practiced, but it is perfectly useless for us to explain or discuss Zazen only verbally.
However, actually speaking, people usually like to speak or discuss Zazen verbally, but exactly speaking, people usually do not like to practice Zazen actually.
And so Master Dogen proclaimes that "Do practice Zazen actually." That is just the meaning of words "Shikan Taza."