Vincent's NT Word Studies
4. Who (oitinev). The double relative, with an explanatory force: seeing that they.Laid down their own necks (ton eautwn trachlon upeqhkan). Laid down is, literally, placed under (the axe). Whether the expression is literal or figurative, or if literal, when the incident occurred, cannot be determined.
Robertson's NT Word Studies
16:4 {Laid down their own necks} (ton heaut"n trachelon hupethkan). First aorist active of hupotiqemi, old verb to place under (the axe of the executioner), only here in N.T. in this sense, though in #1Ti 4:16 to suggest. If literal or figurative, the incident may be connected with the uproar created by Demetrius in Ephesus. Certainly Paul felt deep obligation toward them (see #Ac 20:34). {Not only I} (ouk egw monos). Rather, "not I alone" (adjective monos). The Gentile churches also (great mission workers).