{Mansions} (monai). Old word from men(935c), to abide,
abiding places, in N.T. only here and verse  23 . There are many
resting-places in the Father's house (oikia). Christ's picture
of heaven here is the most precious one that we possess. It is
our heavenly home with the Father and with Jesus. {If it were not
so} (ei de m(885c)). Ellipsis of the verb ( Mr 2:21  Re 2:5,16  Joh
14:11 ). Here a suppressed condition of the second class
(determined as unfulfilled) as the conclusion shows. {I would
have told you} (eipon an humin). Regular construction for this
apodosis (an and aorist--second active--indicative). {For I go}
(hoti poreuomai). Reason for the consolation given, futuristic
present middle indicative, and explanation of his words in
 13:33  that puzzled Peter so ( 13:36f. ). {To prepare a place
for you} (hetoimasai topon humin). First aorist active
infinitive of purpose of hetoimaz(935c), to make ready, old verb
from hetoimos. Here only in John, but in  Mr 10:40  ( Mt
20:23 ). It was customary to send one forward for such a purpose
( Nu 10:33 ). So Jesus had sent Peter and John to make ready
(this very verb) for the passover meal ( Mr 14:12  Mt 26:17 ).
Jesus is thus our Forerunner (prodromos) in heaven ( Heb
6:20 ).