The danger of false doctrine.
God is Spirit and if you're not worshipping Him in Spirit and in Truth, then you are not worshipping God.
King James Bible
But in vain they do worship me, teaching
for doctrines the commandments of men.
21 Jesus said to her, “Woman, believe Me, the hour is coming when you will neither on this mountain, nor in Jerusalem, worship the Father. 22 You worship what you do not know; we know what we worship, for salvation is of the Jews. 23 But the hour is coming, and now is, when the true worshipers will worship the Father in spirit and truth; for the Father is seeking such to worship Him. 24 God
is Spirit, and those who worship Him must worship in spirit and truth.”
25 The woman said to Him, “I know that Messiah is coming” (who is called Christ). “When He comes, He will tell us all things.”
26 Jesus said to her, “I who speak to you am
He.”