Res and of course Tom~: Nice job on explaining the issues.
As noted, the key aspects of who can do what revolve on the Sacraments. The teaching authority is also involved. But to make clear what’s being said, let me start with an analogy.
Army Colonel walks on base, enters a building, notes Airman Doors posting here, and orders him to sign off. Airman Doors ignores him. Who’s right?
The answer is, Airman Doors, assuming that he is not in the wrong for being logged on here due to orders of the day here from his own lawful superior. (My assumption is, he’s manning a desk that requires someone on duty in case of emergency, and at his leisure while on duty to entertain himself pending such an emergency.)
And the colonel is out of line – because as an Army man he has no delegated authority to give orders to an Air Force N.C.O.
In ecclesiology, the delegated authority of Christ to particular human beings is referred to by the term “faculties.” As a committed Christian layman, Tom~ or I have the right and the duty to report the truth of our faith’s teachings accurately to anyone interested, here on the board and in real life, and by word and deed to witness to Christ in our lives.
But we have not been given the faculties to perform six of the seven sacraments, nor to teach authoritatively in our churches. Scholarly laymen can be given such faculties; university professors and “religious” (friars, teaching brothers and sisters, etc.) are specifically designated to teach with the authority of the church behind them, and will often preach at a Sunday service at the request of the pastor or bishop.
Such faculties are derived from the authority Jesus gives the apostles after the Resurrection – see the end of Matthew and John’s gospels as good starting points to explain this. There is documented extrabiblical evidence for this having been handed down (as well as Paul’s commissioning of Titus as Bishop of Crete, strongly implied in the letter to him and IIRC mentioned explicitly elsewhere). Most notably, St. Irenaeus notes that his authority as bishop was given him by my namesake, who in turn was set aside by “the apostles” and consecrated bishop by St. John the Beloved Disciple. And I can trace my confirmation back from the bishop who equipped me with the Holy Spirit in that ceremony for the work of a Christian layman, to the presiding bishop who ordained him, back through presiding bishops of the Episcopal Church, Archbishops of Canterbury, and so on, to St. Theodore of Tarsus, an early Archbishop of Canterbury, whose authority can be traced back to Irenaeus, Polycarp, John, and Jesus.
One can, of course, set up hypothetical situations galore. A series of natural disasters could, for example, kill off every bishop. (In point of fact, the three bishops of the Lutheran Church of Finland, which did preserve the apostolic succession, all died within a few months of each other at the end of WWI; Anglican bishops were called in to consecrate ordained pastors as bishops to restore the succession.)
But the idea is that to perform certain sacraments and to preach authoritatively one must be set apart to do those jobs, ideally with training in doing them properly.
Airman Doors has no more right in his own person to fly over and bomb Baghdad than do I or december or TubaDiva. But in compliance with legal orders he would not only have the right but the duty to do so – presumably after appropriate training – as an A.F. N.C.O. in position to do so.
It’s in that context that “only a bishop may ordain, only a priest or bishop may consecrate the elements of the Eucharist” and so on. My bishop could license me to preach, perform baptisms, and so on as a layman if he so choose, being convinced of my sincerity and ability to do so. By doing this, he would be equipping me with the faculties to licitly do these jobs in Christ’s name. Until he does, I may not in good conscience do them.