The Gemara on today’s daf discusses a case where a person accepts upon himself two consecutive periods of nezirut (under ordinary circumstances, a nazir must go thirty days without cutting his hair, drinking wine or coming into contact with the dead – see Bamidbar chapter 6). If, upon completing the first thirty days the nazir successfully petitions to have his first vow of nezirut annulled, then the time that he kept the laws of nezirut will be applied to his second vow and he has completed his obligation.
At first the Gemara tries to limit this ruling to a situation where the first nezirut was not fully completed, e.g. cases where the final sacrifices had not yet been brought, or the closing ceremony of cutting the nazir‘s hair had not yet be fulfilled. Rav Ashi, however, rejects these limitations and argues that the case of a nazir is unique, since it is only the first nezirut that keeps the second one from beginning. Once the first one is removed the second one can replace it.
Rav Ashi’s explanation is understood in a number of different ways.
Rashi explains that even though this person had fully completed his first commitment as a nazir, nevertheless that vow still remains inasmuch as it keeps the second vow of nezirut from beginning. Once the first vow is removed, the second one immediately takes effect. The Ritva suggests that there is an element of fulfillment of the second vow of nezirut even during the period when the first nezirut is taking place. Therefore we view the two commitments as somewhat intertwined and we do not distinguish between the counting of the days for the first vow or for the second vow. Thus, when the first vow is annulled, it is clear that the second vow of nezirut has already been fulfilled and there is no need to complete it a second time.