The Greek conjunction και is one of those words that seems easy to understand (it means “and”, right?) and then again not so easy (“Why is there a και here?”). From my reading and study,* και is essentially additive, and one forgets this at his peril when evaluating και in context.
Here’s a simple example from Didache 7.4 to reinforce the basic idea.
πρὸ δὲ τοῦ βαπτίσματος προνηστευσάτω ὁ βαπτίζων καὶ ὁ βαπτιζόμενος καὶ εἴ τινες ἄλλοι δύνανται· κελεύεις δὲ νηστεῦσαι τὸν βαπτιζόμενον πρὸ μιᾶς ἢ δύο.
I’ll leave other aspects of the information structure to Steve Runge (though there is some cool stuff, notably the prepositional phrase before the primary verb forming a temporal frame and also the function of δε linking to previous the previous clause indicating development). Here’s the same formatted a bit differently with translation below:
πρὸ δὲ τοῦ βαπτίσματος
And before the baptism
προνηστευσάτω
he should fast beforehand
ὁ βαπτίζων
the one baptizing
καὶ ὁ βαπτιζόμενος
and the one being baptized
καὶ εἴ τινες ἄλλοι δύνανται·
and any others who are able.
κελεύεις δὲ νηστεῦσαι τὸν βαπτιζόμενον
Call upon the one being baptized to fast
πρὸ μιᾶς ἢ δύο.
beforehand one or two days.
There is some interesting text-critical and form-critical stuff going on here, but my interest isn’t (immediately) there. Read Niederwimmer for those details. Regarding και, my interest is in simply seeing how a group is formed using και to add one group element to the existing, known group. While I translated “and” above, you could also do something like “along with” or even “and also”.** The important bit about καιʼs function here is that after the initial group element is introduced (“the one baptizing”), και is used to build that up.
If we just have και associated with the gloss “and” in our minds, we may pass the test and translate the above correctly. But has it been understood? Understanding what function words like και (and δε, and my favorite, αλλα) are up to allows us to better approach the Greek text as Greek instead of as a jumbled set of wooden, English, yoda-speak glosses that need to be decoded and smoothed over in order to be understood.
* Most helpful have been portions of Steve Runge's Discourse Grammar, Heckert's Discourse Function of Conjoiners in the Pastoral Epistles (amazon.com), and Denniston's Particles (amazon.com).
** Ehrman really scrambles the word order to work a “both … and” into it: “But both the one baptizing and the one being baptized should fast before the baptism, along with some others if they can.”