"I saw that God has honest children among the nominal Adventists and the fallen churches, and before the plagues shall be poured out, ministers and people will be called out from these churches and will gladly receive the truth. Satan knows this; and before the loud cry of the third angel is given, he raises an excitement in these religious bodies, that those who have rejected the truth may think that God is with them." {EW, p 261}.

"Souls that were scattered all through the religious bodies answered to the call, and the precious were hurried out of the doomed churches, as Lot was hurried out of Sodom before her destruction.
” --{See Revelation 14:12, Revelation 18, Joel 2:9-11; The Great Controversy Chapter 34}

The most fearful news here is the prophecy that those who will reject the call to come out of the SDA churches and the fallen churches will experience an 'excitement', coming from Satan to deceive them into thinking that 'God is with them".

How do we know from inspired writings that we are now living just before the 'plagues shall be poured out' and therefore have to separate from the fallen Babylonian SDA church and the other churches as well?

We know that we are in just this 'critical time' because of the wild spreading of the 'celebration' style of worship in the SDA churches and the other fallen churches around the world, as accurately predicted by Ellen White.

"The things you have described as taking place in Indiana, the Lord has shown me would take place just before the close of probation. Every uncouth thing will be demonstrated. There will be shouting, with drums, music, and dancing. The senses of rational beings will become so confused that they cannot be trusted to make right decisions. And this is called the moving of the Holy Spirit." {2SM, p 36}.