Now these are the generations of {k} Pharez: Pharez begat Hezron,

(k) This genealogy is brought in to prove that David by succession came from the house of Judah.

Jamieson-Fausset-Brown Bible Commentary

18-22. these 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.

Matthew Henry's Concise Commentary

4:13-22 Ruth bore a son, through whom thousands and myriads were born to God; and in being the lineal ancestor of Christ, she was instrumental in the happiness of all that shall be saved by him; even of us Gentiles, as well as those of Jewish descent. She was a witness for God to the Gentile world, that he had not utterly forsaken them, but that in due time they should become one with his chosen people, and partake of his salvation. Prayer to God attended the marriage, and praise to him attended the birth of the child. What a pity it is that pious language should not be more used among Christians, or that it should be let fall into formality! Here is the descent of David from Ruth. And the period came when Bethlehem-Judah displayed greater wonders than those in the history of Ruth, when the outcast babe of another forlorn female of the same race appeared, controlling the counsels of the Roman master of the world, and drawing princes and wise men from the east, with treasures of gold, and frankincense, and myrrh to his feet. His name shall endure for ever, and all nations shall call Him blessed. In that Seed shall all the nations of the earth be blessed.