Or HaChaim on Deuteronomy 32:2/אור החיים על דברים ל״ב:ב׳

1 יערף במטו לקחי, "May my teaching drop like the rain." We may understand these words of Moses as being similar to the statement in Avot 3,21: "if there is no flour there will be no Torah, etc." The message is that just as the Israelites require rainfall for their physical survival so they require words of Torah instruction for their spiritual survival. The meter of the verse is: "May my teaching drop like rain." G'd does not expect His people to study Torah until He has provided physical sustenance for them. Conversely, you may conclude from Moses' words that if words of Torah will not drop from the people's lips, G'd in turn is not anxious to provide rain for them. This is precisely what Rabbi Eleazar ben Azaryah meant in Avot when he said on the one hand: "if there is no flour there is no Torah; if there is no Torah there will be no flour." Accordingly, you can understand what Rabbi Eleazar ben Azaryah said in this vein: "if you observe that there is not enough flour, know that the reason is that there is not enough Torah study." The reason that Moses employs the simile of rain falling for describing Torah study is because just as rain falls in droplets so Torah is absorbed a little at a time.

2Another reason why Moses chose the simile of rainfall to describe Torah study may have been to alert his listeners that just as the absence of rainfall for a prolonged period would result in death for those deprived of it, so the absence of Torah for a prolonged period would also bring death in its wake. It is similar to what Isaiah said in Isaiah 1,19: "if you agree and give heed, you will eat the good things of the earth; but if you refuse and disobey, you will be devoured by the sword." לקחי, אמרתי, Moses repeats the message in different words in order to make them apply to the two Torot, i.e. the written Torah as well as the oral Torah. Moses aims the word לקחי at the written Torah whereas he refers to the oral Torah when he tells the people to listen to his אמרתי. Moses referred to the Torah G'd had handed him personally, written by G'd's own finger. Although G'd only gave him two tablets containing Ten Commandments, these Ten Commandments contained within them everything that is written in the entire Torah, compare (Bamidbar Rabbah 13). As to the oral Torah, Moses used the term אמרתי, seeing the oral Torah was received by Moses from G'd on a mouth to mouth basis. It was not recorded in writing. Moses labelled the written Torah מטר, rain, whereas he labelled the oral Torah טל, dew. The reason he did this is because the written Torah is the more important of the two. It is the foundation of everything. The oral Torah is a collection of details none of which were spelled out clearly enough in the written Torah. What appears in the oral Torah has only been hinted at in the written Torah. This is why the Torah (Moses) describes the written Torah as rain which is basic and fundamental to nature. Dew, on the other hand, is something which improves the basic work of rainfall just as the oral Torah rounds out the written Torah.

3There is another aspect to the choice of Moses' similes, one that is best understood by the Kabbalists. Please read the comments of the Beer Heytev on Orach Chayim chapter 238 where he quotes the Ari Zal. The author claims that the preoccupation with the study of the written Torah is an obligation which applies only during the day and not during the night. Therefore it is not in order to read the written Torah at night. We have a Baraitha in Midrash Tehillim that during the 40 days that Moses was in heaven, close to G'd, he was able to distinguish between night and day only by means of the subject matter G'd taught him. When G'd taught Moses Mishnah, i.e. oral Torah, he knew it must be night-time. The reason is that it was not permitted to study the written Torah at night.

4This is the reason why Moses described the written Torah as rain, something which does not fall every day, at all hours, only during the rainy season but not during the summer. We have already described several times what happened to the Amora Rava (Taanit 24) who prayed to heaven in order that there be a rainfall in summer because he wanted to prove to a scoffer that G'd can make rain in summer. Similarly, the written Torah is described as rain. Our sages allocated only certain parts of the day to its study, by day and not by night. Dew, on the other hand, is something which we observe on a year round basis, day in day out. It descends both in summer and in winter. Similarly, the oral Torah is described as dew. It is to be studied both by day and by night. There is no restriction on what is a good time to study the oral Torah. The fact that the sun dissipates the effect of the dew is no argument; after all, it is not the fault of absence of dew which on occasion nullifies its effectiveness.

5כשעירים עלי דשא, "like showers on young growth, etc." We may understand this simile in connection with a Baraitha quoted in Midrash Mishley 10. Rabbi Yishmael is quoted as saying that when the time comes when a man has to give an accounting of what he did with his time while on earth, one of the questions he will be asked is if he has a command of the written Torah. If he answers in the negative he is asked why he did not study. Next they ask him if he has a command of the oral Torah. If he answers in the affirmative He is asked whether he also has a command of the Talmud. The questioning continues in that vein. He is not asked whether he has a command of esoterical matters i.e. מעשה מרכבה. They ask a person only on matters which he was capable of studying and absorbing. This is the meaning of כשעירים וכרביבים, meaning that just as G'd makes it rain in little droplets on the grass which is still very young, and in bigger droplets on the grass which has already reached a certain height, one's Torah knowledge is expected to match one's age and one's I.Q. This rule is at one and the same time both harsh and kind. The Torah makes allowances for people who are under-endowed mentally; on the other hand, even someone who has a good command of Scripture, Mishnah and Talmud may be found wanting as he did not measure up to his potential and also studied esoterics, i.e. מעשה מרכבה