Many of us are familiar with Psalm 14:1:
1 THE [empty-headed] fool has said in his heart, There is no God. They are corrupt, they have done abominable deeds; there is none that does good or right.
We all have known an "empty-headed fool" at some point in our lives. There are two very important thing to remember about the "empty-headed fool". Let's look at 1 Corinthians 2:14:
14 But the natural man receives not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned. KJV
Again from the Amplified Bible:
14 But the natural, nonspiritual man does not accept or welcome or admit into his heart the gifts and teachings and revelations of the Spirit of God, for they are folly (meaningless nonsense) to him; and he is incapable of knowing them [of progressively recognizing, understanding, and becoming better acquainted with them] because they are spiritually discerned and estimated and appreciated. AMP
First, there is no way for this person to understand the Word of God, so don't try to "teach" them! Second, because they have no understanding of the Word of God, it is fruitless and useless to try and debate with them! What is REALLY needed? Pray for the eyes of their understanding to be enlightened to the TRUTH that they are personal sinners who need a personal Savior. Then PREACH the Gospel to them! Once they have received Jesus of Nazareth as Lord and personal Saviour, receiving the Holy Spirit to indwell them as Teacher, then they can understand the Word of God, layer upon layer, beginning with the "sincere milk of the Word" (1 Peter 2:2). Continue to pray the prayers of Paul found in Ephesians 1 and 3 and Colossians 1 over them. If they continue in the Word of God, you will have been instrumental in creating a new disciple! Here is an old song by Hillsong United called "Not Ashamed":
Shalom in Him!