Pat asks, "In the practice of circumcision, why did God choose the penis as the place of marking?
As you know, circumcision was essential to the Jewish people beginning with Abraham. It was the distinguishing mark of God’s covenant. Over time the Jews would actually refer to one another as “the circumcised.” Every Jewish boy was circumcised on the eighth day of their life.
Circumcision was intended by God to graphically illustrate man’s depravity. Ever since sin entered the world through Adam, humans have passed on our fallen nature to our children. Because our nature is passed on through procreation, God chose a part of the body that would reflect and illustrate that reality. So, circumcision was primarily a symbol, picturing man’s need to be cleansed from sin at the deepest root of his being.
I’ll take this just a little bit further.
Over the centuries, the Jewish people lost the meaning of this mark. It was intended to point to the need for ultimate cleansing. In practice, at least for many people, it it became merely a ceremony.
And, of course, the mark was set aside in this dispensation of grace. Now in the church age, the seal of the gospel for both Jew and Gentile is the indwelling Holy Spirit.
I hope that helps.