With the phrase stiff-necked people
Stephen is comparing the Jewish leaders to the generation of the wilderness (Exodus 32:9; Exodus 33:3). Like them, they have had the privilege of revelation from God attested by signs and miracles but they have rejected it the same.1 The meaning of uncircumcised in heart and ears
means that they may have the marks of belonging to God’s people (i.e., circumcision), but they have no desire to submit to what he has revealed.
51 “You stiff-necked people, uncircumcised in heart and ears, you always resist the Holy Spirit. As your fathers did, so do you.