Vincent's NT Word Studies
9. Commotions (akatastasiav). From aj, not, and kaqisthmi, to establish. Hence disestablishments; unsettlements. Rev., tumults.Be not terrified (mh ptohqhte). Only here and ch. xxiv. 37.
By and by (euqewv). Better as Rev. immediately.
Robertson's NT Word Studies
21:9 {Be not terrified} (me ptoeqete). First aorist passive subjunctive with me from ptoew an old verb to terrify, from ptoa, terror. In the N.T. only here and #Lu 24:37. {First} (prwton). It is so easy to forget this and to insist that the end is "immediately" in spite of Christ's explicit denial here. See #Mt 24:4-42; Mr 13:1-37 for discussion of details for #Lu 21:8-36, the great eschatological discourse of Jesus