Matthew Poole and continuators on Deuteronomy 25:9

9 Then shall his brothers wife come unto him in the presence of the elders, and loose his shoe from off his foot , and spit in his face , and shall answer, and say, So shall it be done unto that man, that will not build up his brothers house.

Partly as a sign of his resignation of all his right to the woman and to her husbands inheritance; for as the shoe was a sign of ones power and right, Psal. 60 8. and 108. 9. so the parting with the shoe was a token of the alienation of such right, and that he would not and henceforth might not enter upon his brothers land; and partly as a note of infamy, to signify that by this unnatural and disingenuous action he was unworthy to be amongst free-men, and fit to be reduced to the condition of the meanest servants or captives, who used to go bare[illegible: 1+ letters]oot, Isa. 20. 2, 4.

As a return of his contempt upon himself. See Numb. 12. 14. Isa. 50. 6. Mat. 26. 67. and 27. 30. This was not done Ruth 4. either because he was not a brother, but a remoter kinsman, and so deserved less shame; or because Ruth did not prosecute him to the utmost, but freely consented to this exchange.

A phrase oft used for the procreation of children and the increase of a family. See Gen. 16. 2. Exod. 1. 21. 1 King 11. 38. 1 Chron. 17. 25.