The Gemara says that Boaz instituted sheilas shelom chavero beShem, and miShamayim they agreed, as evidenced by the malach saying "Hash-m imecha gibor hachayil".
The pasuk brought as proof was said to Gidon, who lived well before Boaz, so how could it be an agreement to a Takanah that Boaz instituted years later?
If anything it would be a source for Boaz's Takanah, but the Gemara implies that it was his own initiative, not that he learned it from anyone?
Gershon Dubin, Brooklyn, NY, USA
Baruch She-Kivanta! Your question is asked by the Maharsha!
(1) The Maharsha DH u'She'eilas does not answer the question, but an answer is given by the commentary of Maharzav to Midrash Rabbah Ruth Parsha 4 paragraph 5 DH ve'Chein Ha'Malach. He answers that, in fact, this Gemara can be easily understood according to the opinion that the story of Ruth took place in the time of the Judges, Shamgar and Ehud, and in the time of Eglon the King of Moab, who lived before the time of Gidon. The source for this is Midrash Rabbah Ruth Parshah 1:1 DH Vayehi which explains that the first verse in the Book of Ruth "And it happened in the days when the judges judged" refers to the days of Shamgar (see Shoftim 3:31) and Ehud (see Shoftim 3:15). Maharzav in his commentary to 1:1 DH u'Mee explains that "when the judges judged" suggests that there were two judges operating together. This is appropriate to Ehud and Shamgar because Shoftim 4:1 states (after we are told that Shamgar had become the judge) that Ehud had died. We learn from this that there was a period of time when Ehud and Shamgar were alive and judging the people together.
According to this, Boaz also lived before the time of Gidon and therefore when the Malach said to Gidon "Hash-m Imecha Gibor ha'Chayil" this indicated to Gidon that the Beis Din in Shamayim agreed with the Takanahh that Boaz had made earlier on.
(2) However there is an opinion in the Gemara Bava Basra 91a that Boaz and Evtzan are the same person. Since Evtzan was the last of the Judges it is clear that according to this opinion Boaz lived after Gidon, so your question remains difficult. Maharzav answers that according to this opinion we must say that the Gemara is not actually offering a proof that in Shamayim they agreed with the Takanah of Boaz, but rather what we are being taught is that Boaz had made a correct Takanah, because the Malach had already been commanded by Hash-m to bless Gidon with the name of Hash-m, which suggests that Boaz was doing the right thing.
(3) See another answer to your question in Aruch le'Ner.
KOL TUV
Dovid Bloom