Why does it say "Zera Avraham Avdo"?
Radak: This refers to Yisrael, and not other Zera of Avraham. In Divrei ha'Yamim (I, 16:13) it says "Zera Yisrael Avdo"; these are the same. Hashem told Avraham "Ki v'Yitzchak Yikarei Lecha Zara" (Bereishis 21:12), and Yitzchak told Yakov "va'Yiten Lecha Es Birkas Avraham Lecha ul'Zar'echa Itach" (ibid., 28:4). The Zera special to Avraham is Zera Yisrael, like the end of the verse "Bnei Yakov Bechirav."
Malbim: This hints to what Hashem did for Avraham because he was "Avdo", and served Him faithfully.
Malbim (Divrei ha'Yamim I, 16:8): The promise [of the land] was initially to Avraham. In Divrei ha'Yamim I, 16:13 it says "Zera Yisrael", for His wonders with the Aron were due to Yisrael, the father of the nation.
Why does it say "Bnei Yakov Bechirav"?
Radak: This clarifies that "Zera Avraham Avdo" applies only to Yisrael.
Malbim: This shows that He chose them to be His portion - "Yisrael Avdi Yakov Asher Becharticha" (Yeshayah 41:8). Gra (Divrei ha'Yamim I, 16:13) - He chose them when they were still Bnei Yakov 1 .
When Yakov had only sons, but not grandsons. It does not mean before Yakov was called Yisrael, for even after this, he is called also Yakov. (PF)
