Illusions are delusions:

1 Tim. 4:4 Now the Spirit [a]expressly says that in latter times some will depart from the faith, giving heed to deceiving spirits and doctrines of demons, 2 speaking lies in hypocrisy, having their own conscience seared with a hot iron,

2 Tim. 4:3 For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; 4 and they will turn their ears away from the truth, and be turned aside to fables.

Gal.1:6 I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, 7 which is not another; but there are some who trouble you and want to pervert[a] the gospel of Christ. 8 But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be [b]accursed. 9 As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed.

Jude 1:3

Beloved, while I was very diligent to write to you concerning our common salvation, I found it necessary to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints.

Illusions are delusions:

1 Tim. 4:4 Now the Spirit [a]expressly says that in latter times some will depart from the faith, giving heed to deceiving spirits and doctrines of demons, 2 speaking lies in hypocrisy, having their own conscience seared with a hot iron,

2 Tim. 4:3 For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; 4 and they will turn their ears away from the truth, and be turned aside to fables.