"Men professing to have new light, claiming to be reformers, will have great influence over a certain class who are convinced of the heresies that exist in the present age and who are not satisfied with the spiritual condition of the churches. With true, honest hearts, these desire to see a change for the better, a coming up to a higher standard. If the faithful servants of Christ would present the truth, pure and unadulterated, to this class, they would accept it, and purify themselves by obeying it. But Satan, ever vigilant, sets upon the track of these inquiring souls. Someone making high profession as a reformer comes to them, as Satan came to Christ disguised as an angel of light, and draws them still further from the path of right. 5T 144.1"
"For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ."
Both passages discuss false teachers disguising themselves as righteous figures. EGW explicitly mentions Satan as an angel of light, echoing the concept in 2 Corinthians 11:13, which speaks of transforming into apostles of Christ.