Why did HaSh-m not find a more simple way of saving Noach, instead of troubling him to spend 120 years building an ark?
Rashi and Seforno: So that the people would ask him what he was doing, and when he would inform of the impending destruction of the world due to their sins, they would do Teshuvah. 1
Ramban (Bereishis 6:19): To maximize the natural circumstances and to minimize the miracle. 2
Ramban: This is the way HaSh-m generally runs the world. Ramban also points out that, considering the numerous species of animals and birds in the world, among them some as large as elephants, and considering that Noach had to store food for every species of animal that existed, ten arks would not naturally have sufficed to hold them all.
Why was Noach told to use specifically "Gofer-wood"?
Rashi: It is a play on words, since "Gofer" is similar to "Gofris" (sulfur), which HaSh-m used to heat up the water 1 with which He destroyed the world. 2
Riva: How could the pitch stand up to boiling water? It must not have been so hot. Or, near the Ark it was not boiling. We must say so according to the opinion that Og survived through holding onto the Ark.
So He used the same commodity, as it were, to save Noach as He used to destroy the world.
Why was Noach's Ark covered with pitch both on the inside and on the outside, and the basket in which Moshe would later be placed had pitch only on the outside?
Rashi #1: Because, whereas the water of the Flood was turbulent, the water of the Nile was calm, so it for the basket it sufficed to have mud inside.
Rashi #2: So that Moshe the Tzadik should not have to bear the unpleasant smell of pitch. 1
Gur Aryeh: The second approach seems difficult; would Moshe's mother have put him in danger merely due to the bad smell? He answers, the Pasuk in Shemos is describing extra precautions taken by Moshe's mother (otherwise, why mention any smearing at all; surely she must have put some water-proofing on the basket!). According to the first approach, pitch was not necessary on the inside, even as an extra precaution, because the water was calm. According to the second approach, pitch would have been appropriate on the inside as an extra precaution, but she refrained from doing so due to the bad smell.
QUESTIONS ON RASHI
Rashi writes: "Gofer wood is so called... because of the sulfur (Gofris) with which they were to be punished." How do we know that the generation of the Flood was punished with sulfur?
Gur Aryeh: The water was boiling hot, and water that [emerges from the ground] hot is usually sulfurous.
