Concerning the blessing after drinking wine, al hagefen v'al p'ri hagefen, there are those among the Gaonim who hold that one must recite a concluding blessing of thanksgiving after each cup of wine. Our teacher Hai Gaon says: "It is not fitting for us to recite al hagefen after each of the cups of wine since together they constitute one mitzvah and there is no interruption between them so that a blessing at the end should be sufficient. The Rif suggests that we should recite the concluding blessing (al hagefen) after the first two cups of wine and again after the final two cups of wine. The author of Sefer Hahashalamah explains that the Rif's opinion makes sense since the obligation to recite the blessing over the wine before the meal is not canceled by the wine during the meal and the wine after the meal is not exempted from a blessing by the wine during the meal. The reason for this is the purpose of the wine is different. The wine in the meal is for serving (lisharot) while the wine before and after the meal is for the drinking (lishtot). Since the wine lishtot is more important than the wine lisharot, the wine that is drunk during the meal does not divide the first two cups from the second two cups of wine in the Seder, and a blessing can be recited at the end of the Seder for all four cups of wine.