{Till they see the kingdom of God come with power} (he(9373) an
id(9373)in t(886e) basileian tou theou el(886c)uthuian en dunamei). In
 8:38  Jesus clearly is speaking of the second coming. To what is
he referring in  9:1 ? One is reminded of  Mr 13:32  Mt 24:36 
where Jesus expressly denies that anyone save the Father himself
(not even the Son) knows the day or the hour. Does he contradict
that here? It may be observed that Luke has only "see the kingdom
of God," while Matthew has "see the Son of man coming"
(erchomenon, present participle, a process). Mark has "see the
kingdom of God come" (el(886c)uthuian, perfect active participle,
already come) and adds "with power." Certainly the second coming
did not take place while some of those standing there still
lived. Did Jesus mean that? The very next incident in the
Synoptic Gospels is the Transfiguration on Mount Hermon. Does not
Jesus have that in mind here? The language will apply also to the
coming of the Holy Spirit on the great Day of Pentecost. Some see
in it a reference to the destruction of the temple. It is at
least open to question whether the Master is speaking of the same
event in  Mr 8:38  9:1 .