Deficiencies in our ancestors?

On Pesachim 119b, there's an interesting discussion of who will lead the bentching (the blessing after the meal) at the feast when Moshiach (the Messiah) arrives. The honor is first offered to Abraham, who declines because only one of his sons stayed Jewish; then Isaac (ditto); then Jacob, who declines because he married two sisters (which would later be prohibited by Torah law); then Moshe, who declines because he didn't merit to enter Israel even after his death; then Joshua, who declines because he had no children; and finally it is offered to David, who accepts because (says the Talmud) this proves the verse from Psalms (which are ascribed to David): "The cup of salvation shall I raise, and the Name of God I will call upon." (The leader of bentching at a major feast holds a cup of wine during the blessings.)

Rabbi Grossman, who was filling in for Rabbi Elefant on the OU Podcast for that day, brought in a fascinating gloss by the Maharsha: each person who declined did so because the problem that is listed explicitly in the Talmud is a chisaron (deficiency) in one of the areas that we thank God for in the bentching:

• Isaac's covenant is described in the Torah as "b'Yitzchak," which is homiletically expounded as "Since Esau left the covenant, the covenant was only 'in' part of Isaac but wasn't complete with him."
• Jacob's lack was, as explained above, in "the Torah that You teach us."
• Moses never entered the land, which is the subject of the second blessing. (So even though Moses is credited with writing the first blessing when the manna fell, he'd have to stop there.)
• Joshua never had children, and one can read "Uv'nei Yerushalaym" (which means "Rebuild Jerusalem") as "And the children of Jerusalem," which would exclude him.
• David not only had none of these lacks, but his son Solomon built the Temple, fulfilling both senses of "Uv'nei Yerushalayim"

The verse cited above is preceded by "How can I thank God for all the complete wonderfulness upon me?" David was the only one of these, says the Maharsha, who could thank God for all the complete wonders in the betching, and therefore, "The cup of salvation I (David) shall raise, and the Name of God I (David) will call upon."

But R' Grossman didn't explain Abraham's deficiency. Any thoughts?

Deficiencies in our ancestors?

On Pesachim 119b, there's an interesting discussion of who will lead the bentching (the blessing after the meal) at the feast when Moshiach (the Messiah) arrives. The honor is first offered to Abraham, who declines because only one of his sons stayed Jewish; then Isaac (ditto); then Jacob, who declines because he married two sisters (which would later be prohibited by Torah law); then Moshe, who declines because he didn't merit to enter Israel even after his death; then Joshua, who declines because he had no children; and finally it is offered to David, who accepts because (says the Talmud) this proves the verse from Psalms (which are ascribed to David): "The cup of salvation shall I raise, and the Name of God I will call upon." (The leader of bentching at a major feast holds a cup of wine during the blessings.)

Rabbi Grossman, who was filling in for Rabbi Elefant on the OU Podcast for that day, brought in a fascinating gloss by the Maharsha: each person who declined did so because the problem that is listed explicitly in the Talmud is a chisaron (deficiency) in one of the areas that we thank God for in the bentching:

• Isaac's covenant is described in the Torah as "b'Yitzchak," which is homiletically expounded as "Since Esau left the covenant, the covenant was only 'in' part of Isaac but wasn't complete with him."
• Jacob's lack was, as explained above, in "the Torah that You teach us."
• Moses never entered the land, which is the subject of the second blessing. (So even though Moses is credited with writing the first blessing when the manna fell, he'd have to stop there.)
• Joshua never had children, and one can read "Uv'nei Yerushalaym" (which means "Rebuild Jerusalem") as "And the children of Jerusalem," which would exclude him.
• David not only had none of these lacks, but his son Solomon built the Temple, fulfilling both senses of "Uv'nei Yerushalayim"

The verse cited above is preceded by "How can I thank God for all the complete wonderfulness upon me?" David was the only one of these, says the Maharsha, who could thank God for all the complete wonders in the betching, and therefore, "The cup of salvation I (David) shall raise, and the Name of God I (David) will call upon."

But R' Grossman didn't explain Abraham's deficiency. Any thoughts?