Thank you!「坐禅して人か佛になるならハ」
Zazen shite hito ka hotoke ni narunaraba.
Please wait for our experts, but I'd translate this roughly to: "Through zazen, you could become either a person or a Buddha." Meaning you can't reach enlightenment by only focusing on the outer form of zazen and neglecting the spiritual aspects of seeking the right path.
坐禅蛙画賛|収蔵品の紹介「出光コレクション」|出光美術館
idemitsu-museum.or.jp
Thank you!Embedded in this image and the accompanying phrase, is the idea that if zazen was all that was required, then even a frog could become human (because the frog is basically sitting in a zazen-like position all day). So it is a mild admonishment against just following the basic postures of zen.
In other words, what Thomas said above.