Vincent's NT Word Studies
25. When once (af ou). Lit., from the time that. Compare ver. 7. Some editors connect this with the previous sentence: "Shall not be able when once," etc.Whence (poqen). Of what family. Ye do not belong to my household. See John vii. 27: "We know whence he (Jesus) is;" i.e., we know his birthplace and family.
Robertson's NT Word Studies
13:25 {When once} (af' hou an). Possibly to be connected without break with the preceding verse (so Westcott and Hort), though Bruce argues for two parables here, the former (verse #24) about being in earnest, while this one (verses #25-30) about not being too late. The two points are here undoubtedly. It is an awkward construction, af' hou = apo toutou hote with an and the aorist subjunctive (egerqei and apokleisei). See Robertson, _Grammar_, p. 978. {Hath shut to} (apokleisei), first aorist active subjunctive of apokleiw, old verb, but only here in the N.T. Note effective aorist tense and perfective use of apo, slammed the door fast. {And ye begin} (kai arxesqe). First aorist middle subjunctive of arcomai with af' hou an like egerqei and apokleisei. {To stand} (hestanai). Second perfect active infinitive of histemi, intransitive tense {and to knock} (kai krouein). Present active infinitive, to keep on knocking. {Open to us} (anoixon hemin). First aorist active imperative, at once and urgent. {He shall say} (erei). Future active of eipon (defective verb). this is probably the apodosis of the af' hou clause.