ὑπηκούσατε δὲ ἐκ καρδίας εἰς ὃν παρεδόθητε τύπον διδαχῆς (6:17)

Says The clause is compressed: the antecedent τύπον διδαχῆς (typon didachēs) is drawn into the relative clause, so the sense is ὑπηκούσατε τῷ τύπῳ τῆς διδαχῆς εἰς ὃν παρεδόθητε, "you obeyed the form of teaching to which you were handed over." Abbott-Smith gives τύπος here as "form" (Rom 6:17) and διδαχή as "teaching … that which is taught."

Uncertain Who is handed over. This note leans to the readers being handed over to the teaching (BSB "to which you were committed"). Grounds: παρεδόθητε is passive with the readers as subject, παραδίδωμι εἰς is used of persons handed over (1:24, 26, 28), and it matches the change of masters in 6:16–18. The alternative takes it as the teaching delivered to them (KJV), from παραδίδωμι of passing on tradition (1 Cor 11:2, 23; 15:3).

Uncertain Whether the clause is Paul's. This note leans to reading 6:17b as Paul's: it fits the change of masters in 6:16–18. The alternative, that it is a later gloss, rests on its interrupting the contrast of 6:17a and 6:18 (discussed by reference, Cranfield).