why do we Catholics have an ordained Clergy?

All Christians accepted an ordained priesthood for the first sixteen centuries of Christianity.

Christ gave a special mission to His apostles that that all His followers did not share in the same way.

The New Testament refers to three types of offices in the Church: bishops(episkopos), elders(presbyteros), from which we derive the words "presbyter" and "priest") and deacons(diakonos).

"Presbyteros" appears often in Scripture. (e.g. Acts 15:2-6; 21:18; 1Pt 5:1; 1Tm 5:17)

Every Christian is a "priest" in terms of offering the sacrifices of prayer (Heb 13:15), almsgiving (Heb 13:16), and faith in Jesus (Phil 2:17).

1Peter 2:5, 9 and Revelation 1:6 are cited in order to establish thatall Christians are priests.

However, St. Peter was reflecting the language of Exodus 19:6, where theJews were described in tis fashion, but the Jews also had a specialized, professional priesthood, which was drawn fom one tirbe: the Levites.