The Mishna (34a-b) brought two opinions about the amount of grape juice or wine that a nazir must drink in order to be held liable. According to the Mishna rishona (first) the amount is a revi’it (one-fourth of a log), which is the usual requirement for drinking, while according to Rabbi Akiva the amount is a ke-zayit (the size of an olive) which is usually the amount required for solid foods. Our Gemara explains Rabbi Akiva’s position as being based on the passage that forbids drinking wine or other grape products and concludes va-anavim lahim ve-yeveshim lo yokhel – that neither fresh nor dried grapes can be eaten (see Bamidbar 6:3). Since the pasuk concludes with a statement about eating, that defines all of the other categories mentioned, as well.
In truth, there are two approaches to the disagreement between the Mishna rishona and Rabbi Akiva. According to the first, the Mishna rishona rules that the laws of nezirut match the normal laws of eating and drinking, i.e. ke-zayit for eating and revi’it for drinking, while Rabbi Akiva believes that all of the rules of nezirut are based on a ke-zayit. According to the second approach, the Mishna rishona rules that all the laws of nezirut – both eating and drinking – require revi’it, while Rabbi Akiva says that they all require ke-zayit. The reading that appears in our Gemara matches the first approach, while the Rosh accepts the second approach, based on his reading of the Gemara that presents the Mishna rishona (called the Tanna Kamma by our Gemara) as saying that all things forbidden to the nazir are compared to drinking.
The Meiri offers an alternative perspective. He has the reading that appears in our Gemara, according to which the Mishna rishona does not compare all things forbidden to the nazir to drinking, meaning that solid food from grapes cannot be combined with wine or grape juice, since they are separate entities. Rabbi Akiva disagrees, claiming that ke-zayit and revi’it are basically the same amount, just one is for solids and the other for liquids. Given that the pasuk uses the terminology of “eating” also when discussing wine, we learn that with regard to nazir there is no difference between grapes and wine, and they can be combined to add up to the minimum requirement.