A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
rut 4:1BOAZ CALLS INTO JUDGMENT THE NEXT KINSMAN. (Rut 4:1-5)
Then went Boaz up to the gate of the city--a roofed building, unenclosed by walls; the place where, in ancient times, and in many Eastern towns still, all business transactions are made, and where, therefore, the kinsman was most likely to be found. No preliminaries were necessary in summoning one before the public assemblage; no writings and no delay were required. In a short conversation the matter was stated and arranged--probably in the morning as people went out, or at noon when they returned from the field.
rut 4:2he took ten men of the elders of the city--as witnesses. In ordinary circumstances, two or three were sufficient to attest a bargain; but in cases of importance, such as matrimony, divorce, conveyancing of property, it was the Jewish practice to have ten (Kg1 21:8).
rut 4:3Naomi . . . selleth a parcel of land--that is, entertains the idea of selling. In her circumstances she was at liberty to part with it (Lev 25:25). Both Naomi and Ruth had an interest in the land during their lives; but Naomi alone was mentioned, not only because she directed all the negotiations, but because the introduction of Ruth's name would awaken a suspicion of the necessity of marrying her, before the first proposition was answered.
rut 4:4there is none to redeem it beside thee; and I am after thee--(See on Deu 25:5). The redemption of the land of course involved a marriage with Ruth, the widow of the former owner.
rut 4:6HE REFUSES THE REDEMPTION. (Rut 4:6-8)
The kinsman said, I cannot redeem it . . ., lest I mar mine own inheritance--This consequence would follow, either, first, from his having a son by Ruth, who, though heir to the property, would not bear his name; his name would be extinguished in that of her former husband; or, secondly, from its having to be subdivided among his other children, which he had probably by a previous marriage. This right, therefore, was renounced and assigned in favor of Boaz, in the way of whose marriage with Ruth the only existing obstacle was now removed.
rut 4:7a man plucked off his shoe--Where the kinsman refused to perform his duty to the family of his deceased relation, the widow was directed to pull off the shoe with some attendant circumstances of contemptuous disdain. But, as in this case, there was no refusal, the usual ignominy was spared; and the plucking off the shoe, the only ceremony observed, was a pledge of the transaction being completed.
rut 4:9HE MARRIES RUTH. (Rut 4:9-12)
Boaz said unto the elders, Ye are witnesses this day, that I have bought all that was . . . Chilion's and Mahlon's, of the hand of Naomi--Although the widow of Chilion was still living, no regard was paid to her in the disposal of her husband's property. From her remaining in Moab, she was considered to have either been married again, or to have renounced all right to an inheritance with the family of Elimelech.
rut 4:10Ruth the Moabitess . . . have I purchased to be my wife--This connection Boaz not only might form, since Ruth had embraced the true religion, but he was under a legal necessity of forming it.
rut 4:11all the people and the elders, said, We are witnesses--A multitude, doubtless from curiosity or interest, were present on the occasion. There was no signing of deeds; yet was the transfer made, and complete security given, by the public manner in which the whole matter was carried on and concluded.
the Lord make the woman that is come into thine house like Rachel and like Leah--This was the usual bridal benediction.
rut 4:12let thy house be like the house of Pharez--that is, as honorable and numerous as his. He was the ancestor of the Beth-lehem people, and his family one of the five from which the tribe of Judah sprang.
rut 4:17SHE BEARS OBED. (Rut 4:13-18)
rut 4:18these are the generations of Pharez--that is, his descendants. This appendix shows that the special object contemplated by the inspired author of this little book was to preserve the memory of an interesting domestic episode, and to trace the genealogy of David. There was an interval of three hundred eighty years between Salmon and David. It is evident that whole generations are omitted; the leading personages only are named, and grandfathers are said, in Scripture language, to beget their grandchildren, without specifying the intermediate links.