Hello,
Need is the verb in the sentence:
God's people need to be flexible
Remember: A verb describes an action or occurrence. Need is a semi-modal or transitive verb in this context, and need comes first in the verb phase, which is after the subject, followed by another verb.
There are many more different contexts and forms that need could be used in as well. One example is:
Question form:
The use of semi-modal need in this form is uncommon. Whenever it is used in a question form, the tone is formal.
I hope this helped.