With this item, she is essentially saying, "IF you are going to be a 'Christ-follower' then Jesus is the 'new covenant' - represented by baptism (and really, by salvation - grace through faith). Circumcision is not only meaningless in the Christian faith, it is also completely contradictory to Christian faith because it is as though one is saying, "Christ is not good enough for me, so I am going to abide by 'old covenant' ways just in case." It is denying one's grace through faith - salvation in Christ.
Circumcision has absolutely NO place in Christianity.
Of course, Jesus' close followers and the early church clearly understood this. Circumcision was entirely forbidden in the newly formed church, and it remained this way for all of Christian history, until some uninformed parents in the U.S. started cutting their boys in the 20th century (at the urging of Kellogg and Graham to 'cleanse' and 'purify' boys and men). Genital cutting was such a grave offense, in fact, that if someone did cut their baby, they would be ex-communicated from the church. At some points and places in Christian history, if a mother did not protect her infant boy from genital harm, she was deemed guilty on several accounts (against her child and against the church) and was subject to stoning.
We thought many of the responses this tshirt brought about were interesting, so are sharing here as an opportunity for further exploration of the topic.
To obtain ample information regarding the place of genital cutting (or lack thereof) in religious practices throughout history, these books are a great place to start:
Marked in Your Flesh: Circumcision from Ancient Judea to Modern America
Circumcision: A History of the World's Most Controversial Surgery
Questioning Circumcision: A Jewish Perspective
Covenant of Blood: Circumcision and Gender in Rabbinic Judaism
Circumcision Exposed: Rethinking a Medical and Cultural Tradition
Circumcision: The Painful Dilemma
What Your Doctor May Not Tell You About Circumcision
Circumcision: What Every Parent Should Know
A Surgical Temptation: The Demonization of the Foreskin and the Rise of Circumcision in Britain
For additional reading pertaining specifically to Christianity and Circumcision see this page of resources.
Additional resources regarding circumcision (books, articles, online sites) can be found here.