9 then his brother's wife shall go up to him in the presence of the elders, and pull his sandal off his foot, and spit in his face; and she shall answer and say, 'So shall it be done to the man who does not build up his brother's house.'

Matthew Henry's Commentary on Deuteronomy 25:9

Commentary on Deuteronomy 25:5-12

(Read Deuteronomy 25:5-12)

The custom here regulated seems to have been in the Jewish law in order to keep inheritances distinct; now it is unlawful.