“because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened.” Romans 1:21

Look at the first verse, “they knew God.” We are talking about Christians here. In order to know God the Father, we must know the Son, Jesus.

They exchanged the truth of God for a lie, “Therefore God also gave them up to uncleanness, in the lusts of their hearts, to dishonor their bodies among themselves, who exchanged the truth of God for the lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen.” Romans 1:24-25

We must guard our hearts above all things for everything pertaining to life comes from it (Proverbs 4:23). We can have an evil heart or a heart that is glorifying God. We need to prepare our heart to seek the Lord, “And he did evil, because he did not prepare his heart to seek the Lord.” 2 Chronicles 12:14

God searches the earth for those hearts that are loyal to Him (2 Chr 16:9).

“Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; but exhort one another daily, while it is called “Today,” lest any of you be hardened through the deceitfulness of sin. For we have become partakers of Christ if we hold the beginning of our confidence steadfast to the end, ¹while it is said: “Today, if you will hear His voice, Do not harden your hearts as in the rebellion.” Hebrews 3:12-15 NKJV