Ζηλοῦσθαι to be zealously sought, in the same sense as before. It is passive. It is good for you Galatians to be zealously sought. In a good thing (ἐν καλῷ) answers to οὐ καλῶς not honorably, Gal 4:17. In a good matter - the interest of the gospel. Thus Paul would say: “These Judaisers zealously strive to win you over to their views; but they do not do this in an honorable way. There is no harm in seeking to interest and enlist you, provided it is in a good cause.â€