The first part is a declaration about the nature of God. It's like the inverse of Num. 23:19, which tells us what God is not, then goes on to describe his nature (He does not lie, He need not repent, He does what He determines). John 4:24 tells us what God is, then goes on to describe in what manner He is to be worshipped.
It's a lot like the teaching method that tells you a fact, then provides the implications of that fact.