The Torah goes into detail to describe the design of the ark. It details measurements, window, compartments, etc. It then tells us that Noach did exactly as he was instructed by God.
RSRH writes here that he chooses to not comment on whether the size of the ark was large enough and other such questions (Others ask if the ark could endure the harsh flood, the water’s heat and similar questions. GS) God has many ways He brings about salvation.
The lesson to take here is that God chose one man and his family and the animal world. He would save them only if man does exactly as he is commanded.
Contrary to what many think, a person’s actions have value only if they constitute performing God’s will. What a person does on the basis of his own judgement is of secondary, uncertain importance. This is a fundamental principal of Judaism. גדול המצווה ועושה ממי שאינו מצווה ועושה – קדושין דף לא
Man must do his part by fulfilling God’s will and God will do the rest.
Beraishis 6:15-22
pages 182-183
