Dear Joseph:

I praise God that our Q&A was helpful to you.

To your question, the passage is from Mathew 7:6  "Do not give dogs what is holy; and do not throw your pearls before swine, lest they trample them under foot and turn to attack you."

Dogs and swine are derogatory Jewish epithets for pagans. Dogs were mostly wild and were scavengers and pigs, of course, were considered unclean.

To quote from the St. Ignatius Study Bible commentary:

Jesus redirects these insulting labels to anyone inhospitable to the gospel, the Jew or Gentile (cf. Philippians 3:2; Revelations 22:15). [as to the phrase "what is holy"]: In Judaism, holiness characterized anything consecrated for covenant worship. To treat holy articles in a common manner would profane them (Exodus 29:37; Leviticus 22:10-16). Jesus carries the same notion into the New Covenant. The early church applied this statement to the Holy Eucharist, a sacrament rightly withheld from the unbaptized (Didache 9:5).

I would say that modern day dogs and pigs include the unbaptized or baptized who are hostile to Christ, especially those who profane and/or blaspheme the Holy Eucharist (such as comedians and anti-Catholic bigots), the baptized who commit sacrilege against the Holy Eucharist, such as politicians who claim to be Catholic but do not hold to Catholic teaching yet still receive the Holy Eucharist, and dogs are certainly priests who rebel against the Church.

God Bless,
Bro. Ignatius Mary