The son born in the ordinary way is Ishmael. The son born according to promise is Isaac. According to Genesis 21:9, Ishmael ridiculed and mocked Isaac. Paul refers to this incident and says that it is an example of a pattern that has continued since that day.1 The children of the slave (the Judaizers/Jews) focus on the works of the flesh and they resist those who are born of the Spirit, the children of the free (Christians). With their insistence on the need for Gentile believers to be circumcised and submit to old covenant law, the Judaizers are in effect persecuting the Galatian believers.2
29 But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now.