My own understanding of that text is that what is present on earth, a mysterious presence called 'Wicked' shall be consumed ('digested' is quite a good translation of *analisko* [Strong 355][1]) during time, by 'the spirit of his mouth'.

Then, at the end of time, that same Entity will be fully destroyed by the brightness of the glorious return of Jesus Christ to earth.

The 'spirit of his mouth' denotes, to me, what can be referred to as 'his mouthpiece'. It is as though Christ is present on earth, bodily, speaking certain words. 

But he is not, yet, present. There is that which represents him. That is to say, the Christian ministry, those such as Timothy or Titus who are called with an especial vocation to preach and to teach. In the book of the Revelation such are referred to as 'the two witnesses', Revelation 11:3, and their activity, in this same context, may be seen there.

Thus the spirit which goes forth from the mouth of Jesus Christ in heaven, also goes forth on earth by his mouthpieces, to the temporal annihilation of the adversarial Wicked in front of the audience of those who dwell on earth.

The prophets may be seen as performing a similar role, one thinks of Isaiah in particular who, by his words, effectively 'demolished' the adversaries of the Lord.

At the end of time, by the brightness of his coming, the Lord shall eternally destroy the opposition of the Wicked One.

What exactly that 'Wicked' actually is, belongs in another question.






[1]:https://biblehub.com/greek/355.htm