R. Yitzchak says: It is written (Exodus 23:25) "And you shall serve the L–rd your G–d, and He will bless your bread and your water." When is it "your bread"? Before you have eaten it. This tells me only of food as requiring a blessing before it and after it. Whence do I derive (the same for) Torah? R. Yishmael says: It follows a fortiori, viz.: If food, which is only temporal, requires a blessing before and after it, how much more so Torah, which is eternal!