In Matthew there are 2 instances where Jesus said "to be perfect" (both rendering the Greek word τέλειοι).
Matt 5:48: Sermon on the Mount about loving our enemies, directed to the whole audience:
"Be you therefore perfect, as also your heavenly Father is perfect."
Matt 19:21: Jesus replying the rich man who asked Him how to get everlasting life:
"Jesus saith to him: If thou wilt be perfect, go sell what thou hast, and give to the poor, and thou shalt have treasure in heaven: and come follow me."
In my understanding of the Catholic tradition, the 1st one is a "precept" (binding for every Catholic) but the 2nd one is a "counsel", only for those called to a religious life taking the vows of povery, chastity, and obedience. (See the Catholic Encyclopedia article Evangelical Counsels).
While I understand the logic behind the teaching (which I happen to agree personally), what is the exegetical warrant for the two different interpretations & applications of the same word? Isn't perfect supposed to be the same for everyone?
Possibly relevant: Protestant's objections to the "two-tiered system".