International Standard Bible Encyclopedia (1915)

As it is figuratively used, both in the Old Testament and in the New Testament, the word means "stubborn," "untractable," "not to be led." The derivation of the idea was entirely familiar to the Jews, with whom the ox was the most useful and common of domestic animals. It was especially used for such agricultural purposes as harrowing and plowing (Jud 14:18; 1Co 9:9).

The plow was usually drawn by two oxen. As the plowman required but one hand to guide the plow, he carried in the other an "ox-goad." This was a light pole, shod with an iron spike. With this he would prick the oxen upon the hind legs to increase their speed, and upon the neck to turn, or to keep a straight course when deviating. If an ox was hard to control or stubborn, it was "hard of neck," or stiff-necked. Hence, the figure was used in the Scriptures to express the stubborn, untractable spirit of a people not responsive to the guiding of their God (Ex 32:9; 33:3; De 9:6; 2Ch 36:13; Jer 17:23, etc.). See also the New Testament where sklerotrachelos, is so translated (Ac 7:51), "Ye stiff-necked and uncircumcised in heart and ears, ye do always resist the Holy Spirit.". Compare Baruch 2:30,33.