See verse 31. The warning is most sober! Faithful members of the Church have in many instances been deceived, their faith weakened, and their discipleship diluted through the mingling of scripture with the philosophies of men.
The marriage of Zion and Babylon is an unholy union; it is a vain attempt to harmonize and integrate disparate kingdoms. In the quest for peace between warring ideologies gospel principles are compromised and costly concessions made.