Ex opere operato and baptismal regeneration

Yes to regeneration, but no to the principal of 'ex opere operato'.

With the understanding of Baptism as a work God does to save sinners.

It's effective no matter what. (assuming that the community means what the words mean; we're not talking about Mormon baptisms here) HOWEVER, it's effective as a promise to be believed, not some magic thing that saves you without your knowledge. Basically, baptism says: "you're saved in Christ!" and I say: "oh good, what a relief! Thanks be to God!" but if I abandon God and become an atheist or something it won't help me. (it still counts though. If I come back, that was my one baptism, I don't need a new one.)

In most cases, the difference between Lutheranism and other protestants is something like this:
Protestants: "Believe so that you'll be saved!"
Lutherans: "Believe! You're saved!"
This is why baptism might look like an ex opere operato thing in Lutheran circles, but without faith it's pointless.

Greenham said:

Could you elaborate? What is the Lutheran equivalent/alternative to ex opere operato? What does sacramental efficacy depend on?

Click to expand...

The efficacy of Baptism depends upon, and solely upon, the Word of God. The Word of God always accomplishes the purpose God sends it out to accomplish.