Why is "v'Arbeh" missing a Hei?
Rashi citing Yerushalmi Pesachim 10:5: I made for him many quarrels and tests before giving to him seed. Radak
Why does it mention increasing Avraham's seed here? They became numerous only later!
Malbim: I increased his seed to enable casting off the chaff, i.e. Yishmael and Esav, and only the Pri Kadosh (Yitzchak and Yakov) remained.