People will tell you that they believe in God, yet they do not live out that belief any way near what would line up with the Word of God. But this may not necessarily be an intentional or conscious lie on their part.
The god that many “believe in” is often a compilation of preferences, images, stories, and myths we’ve heard and molded into a deity that we can wrap our heads around, accept, and worship. This god is not necessarily the God we come to know from The Bible, the God who desires an intimate relationship with His creation, the God who brings light out of darkness, the God who brings life out of death, the God who brings order out of chaos, the God whose law is perfect, a law in which His worshipers meditate day and night.
Deuteronomy 6:5-9; Joshua 1:8; Psalm 1:1,2; Proverbs 6:22
For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.  For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.  Claiming to be wise, they became fools,  and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things.  Therefore God gave them up in the lusts of their hearts to impurity, to the dishonoring of their bodies among themselves,  because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen.Romans 1:20-25 ESV