Well, you might want to mention how to follow those feast days now are unnecessary because they were all in expectation of Jesus Christ, who is the Messiah. To follow those and other precepts laid out before the fulfillment of the Law would be akin to saying that one still expects a Messiah, which of course is blasphemy. The Church recognizes that, that is why it is outlawed for anyone to observe those feast days with the intention of an Old Testament Jєω. Which, frankly put, is to not observe these feasts at all.
For example, why is it unnecessary to follow Passover? Well, Jesus Christ, in His bloody Sacrifice at Golgotha, became the Lamb without blemish. The lamb in Passover was superseded by Jesus Christ, Agnus Dei, the Perfect and Spotless Sacrifice. Thus, there is no reason to keep killing lambs in expectation of a Messiah that has already died and rose again. To do so is absurd in the eyes of a Catholic. This now became the Sacrament of the Eucharist.
Why do we not observe the feast of Tabernacles, also? This is because Christ fulfilled this feast by fasting 40 days in the desert (this feast commemorated the 40 years the Israelites were in the desert), and overcoming the devil by means of rejecting his various temptations presented to him. This now, as we are in currently, became the observation called Lent.
Also, why is there no difference between circuмcision and uncircuмcision? Jesus Christ perfected this by instituting the Sacrament of Baptism, which is the fulfillment of circuмcision, leaving an indelible spiritual mark, as opposed to an indelible fleshly mark.
The Church has plenty of beautiful feast days to celebrate. My favorite being the feast day of Ss. Peter and Paul, on June 29th.
Remember as well these two key factors:
a) It was your friend's decision to accept the reality of Christ, then to reject Him.
b) St. Paul tells us to admonish those in error one to two times. After that, we must avoid them as a "heathen and a publican".