How is he blessed?
Torah Temimah citing Rus Rabah: Bo'az was 80 years old and had no children, but once Na'ami prayed for him, immediately he was Nifkad 1 .
Vilna Gaon: He is blessed that Hashem summonsed for him such a great Mitzvah [to sustain you when you were so hungry - refer to 2:19:4:1]. It is famous that he is blessed to Hashem!
Perhaps this means that it was immediately decreed that he would have a son from Rus. He married her at the end of the harvests of barley and wheat (three months later - refer to 2:23:1:1)! This Midrash implies unlike Bava Basra 91a, which says that he had 60 children before this, and all died in his lifetime. (PF)
What is the Chesed with the living and with the dead?
Rashi 1 : He feeds the living and takes care of the needs of the dead.
Malbim: Bo'az did not abandon Chesed with the living - Na'ami understood that he did so in order to finance Na'ami and Rus honorably. He will do Chesed with the dead - he will do Yibum, for the good of the Nefesh of the Mes.
Rus Rabah 5:10: He feeds the living and provided the shrouds of the dead. Maharzu [on the Midrash] - Machlon and Kilyon's widows asked Bo'az, who provided shrouds for his relatives. (If so, why did Na'ami need to tell Rus (2:20) that Bo'az is their relative? - PF) Radal - according to Rashi, Bo'az consoled the relatives. According to the Midrash, he provides shrouds for other Mesim. Etz Yosef - Hashem enabled the widows to provide shrouds.
How can he be "Karov Lanu"? Rus, a convert, has no relatives!
Toras Moshe (Bamidbar, Rus DH Gam Ki): He is a Yavam; Yibum applies [not only to a brother, rather, even] to [other] relatives 1 .
Ramban (Bereishis 38:8) said so about before Matan Torah. However, at Matan Torah, Yibum with other relatives was forbidden! (PF)
Why did she say "Karov Lanu ha'Ish mi'Go'alenu Hu"?
Malbim: She explained, "Karov Lanu" - therefore he does Chesed with his living relatives. Chesed with the dead - "mi'Go'alenu Hu" - the Go'el must do Yibum, to redeem the Nefesh of the Mes, lest his name be obliterated from Yisrael.
