In Pergamos we have the reference to Balaam, which will have its counterpart in a yet future day.
Through |the counsel of Balaam| (Num. xxxi.16, etc.) Israel was entrapped and led into the worst form of Midianitish idolatry, when |Israel joined himself unto Baal-peor| (Num. xxv.3).
In the coming future day Pergamos will be in a special manner the seat (or throne) of Satan (ii.13; and compare xiii.2), and a form of idolatry more awful than that of Baal-peor will be on the earth. Peter, writing to the Dispersion, tells of this future time in 2 Peter ii., and in verse 15 he speaks specially of their |following in the way of Balaam the son of Bosor.|
Jude also connects his description of a similar phase of idolatry with |the error of Balaam| (verses 10-13).
It is clear, therefore, that that special feature of idolatry connected with Balaam's |counsel| is referred to in Rev. ii.14, and will be revived in the period described in the Apocalypse.
And, as, upon this great evil the special judgment of the |sword| was sent and executed (Num. xxxi.1-15), so here. He who speaks to the same People of the same evil, speaks also of the same judgment, |I will fight against them with the sword of my mouth| (Rev. ii.16), which threat will be carried out in chap. xix.21. This is why we have that special mention of the |sharp sword,| describing the speaker in ii.12, referring to the same feature of the Vision as seen in i.16.