פירוש על פסחים 10:7

ברכת שיר – there are those who say, “The soul of all that lives [shall bless Your name]…” and there are those who say, “All Your works will praise You….” And it is has become the practice to recite both.

Introduction This mishnah discusses the third and fourth cups of wine and the conclusion of the meal.

בין שלישי לרביעי לא ישתה – so that he not become inebriated and further, he would be unable to complete the Hallel (i.e., Psalms 113-118).. And if one would say that he is already inebriated, for he drank to his desires during the course of the meal, wine that is partaken of during the meal does not make one drunk; wine after the meal makes one drunk.

They poured him a third cup, blesses over his meal. The Grace after the Meal, or Birkat Hamazon, is recited over a third cup of wine. We should note that according to the Mishnah and Talmud Birkat Hamazon is normally recited over a cup of wine, meaning that one holds a cup of wine while reciting the Birkat Hamazon, then recites a blessing over drinking wine (borei peri hagefen) and then drinks the cup at the end. Some people still have this custom today, at least on Shabbat and festivals.

A fourth [cup], he concludes the Hallel, and recites over it the blessing of song. The fourth cup is recited over the recitation of the Hallel. In the Talmud there is a debate over what the “blessing of the song” is. Some say it is “Nishmat Kol Hai”, a prayer recited during the morning prayers of Shabbat and festivals. Others say it is “Yehallukhah Adonai Elohenu”, which is a prayer recited at the end of Hallel on other occasions. Today we recite both.

Between these cups if he wants he may drink; between the third and the fourth he may not drink. Between the second and third cups it is permitted to drink more wine. This is the time when the meal is consumed and it was allowed to drink extra cups during the meal itself. However, it is forbidden to drink between the third and fourth cups lest he gets drunk and is not able to complete the seder. The rabbis thought that drinking alcohol while eating would not cause one to get drunk.