There is a mistake by Provisionists (e.g., McGrew, the Provisionist Perspective, Leighton Flowers, etc.). To think that Calvinists think that unbelievers can have no knowledge of God whatsoever. The issue comes from misunderstanding claims about total depravity and total inability. Leighton started that trend and it seems many are starting to catch what was already exposed several years ago. But this is an example of an actual understanding of the issue:

By way of contrast, the person without the Spirit – that is, ‘the natural person’ (psychikos anthrōpos, esv) – does not welcome the words that come from the Holy Spirit. The ‘natural person’ refers here to unbelievers since, as noted previously, a Christian, by definition, is a person of the Spirit (cf. Jas 3:15; Jude 19). Paul’s message is not like the mystery religions in which truth is conveyed only to the elite. Instead, those who do not believe also hear the things of the Spirit, but they do not accept them because the message is deemed to be foolish. It is not that unbelievers cannot mentally grasp or comprehend the message of the gospel. Paul’s point is that they do not welcome or receive the message because it strikes them as manifestly untrue. In other words, unbelievers do not grasp the significance of the message proclaimed. Indeed, they are unable to understand the truth and significance of the gospel because such things can be discerned only through the Spirit. Human beings lack the innate capacity to appreciate and receive spiritual truths; only those who have the Holy Spirit can grasp the things of the Spirit.

Schreiner, Thomas R.. 1 Corinthians (Tyndale New Testament Commentaries) . InterVarsity Press. Kindle Edition.

Notice how Dr. Schreiner isn’t alone on this point that I pointed out to Leighton in a conversation:

The Natural Man: Calvinism and the Ability to Understand – The Council (spirited-tech.com)

Warren McGrew on the Natural Man – The Council (spirited-tech.com)

Commentators point out the connections between the natural man and those that reject the Gospel (1:18-24), the need for the Spirit to believe these things, and the term psychikos is most likely referring to unbelievers:

The perception of the things of God’s Spirit as folly (μωρία) recapitulates the parallel theme in 1:23, where the context of the things of the Spirit, namely a crucified Christ (1:23) is an affront (σκάνδαλον) to Jews and folly (μωρίαν) to Gentiles. This provides the reason why (cf. γάρ, for …) the person who lives on an entirely human level rejects them. At this stage of the argument Paul says that such a person does not receive, i.e., rejects, the things of the Spirit, not at this point that such a one cannot receive them. They are rejected because within the prior horizons of these preexisting interests and concerns the message of the cross and the things of the Spirit find no desired relevance or credibility; they are folly unless or until the Spirit moves or expounds those horizons.
This now precisely defines the sense in which a person in this condition cannot come to know them (οὐ δύναται γνῶναι).

Anthony C. Thiselton, The First Epistle to the Corinthians: A Commentary on the Greek Text, New International Greek Testament Commentary (Grand Rapids, MI: W.B. Eerdmans, 2000), 270.

The natural man is most easily defined negatively: he is a man who has not received the Holy Spirit. His natural resources, for example his intellectual resources, are, or may be, complete; he is not in any ordinary sense a ‘bad man’, or a foolish man, or an irreligious man. But lacking the Spirit of God he cannot apprehend spiritual truths, for to him they are foolishness, and he cannot know them, because they are investigated spiritually. This is not simply a matter of inspiration. The Spirit of God is the Spirit of Christ crucified, and the wisdom taught by the Spirit is the word of the cross (1:18), and to the natural man this is foolishness, for it inverts the values by which he lives

C. K. Barrett, The First Epistle to the Corinthians, Black’s New Testament Commentary (London: Continuum, 1968), 77.

“Those who are spiritual” is a reference to all believers; if not all Christians are “mature,” all have the conditions for such growth, thanks to the Spirit. “The person without the Spirit” refers to non-Christians. “The worldly” in 3:1 refers to those made of “flesh,” who are part and parcel of fallen humanity from Adam and so vulnerable to sin. “Infants in Christ” are new Christians, those who have the Spirit and thus a capacity for welcoming spiritual truth and experiencing growth but as yet limited experience of it. And “the worldly” in 3:3 are those who belong to the “flesh,” that is, people who are not only part and parcel of fallen humanity but also continue to live according to its ways.

Roy E. Ciampa and Brian S. Rosner, The First Letter to the Corinthians, The Pillar New Testament Commentary (Grand Rapids, MI; Cambridge, U.K.: William B. Eerdmans Publishing Company, 2010), 135.

In v. 14, Paul puts the spiritual person side by side with the natural person: But, in contrast to those who are spiritual, the natural person (i.e., the person without the Spirit) does not welcome (an understatement explained by the remainder of v. 14) the things that come from the Spirit of God (i.e., God’s full wisdom in planning and providing redemption through Christ crucified and its implications for living). The reason for this rejection is that such a person judges this message to be foolishness. The person without the Spirit is volitionally prejudiced against it, and rejects it in unbelief. In fact, in as negative a statement as you can find in Paul’s letters about the human condition outside of Christ, he says that the person left to their own “natural” devices “is not able to know them,” that is, to respond positively to the things of the Spirit.68 In this regard, the “natural person,” someone belonging to this age and not the age to come, resembles “the rulers of this age,” who in 2:8 also failed to “know” or “understand” the cross. The reason for this inability is that the things that come from the Spirit of God are discerned or “inquired into” only by the aid of the Holy Spirit, whom “the natural person” does not have.

Roy E. Ciampa and Brian S. Rosner, The First Letter to the Corinthians, The Pillar New Testament Commentary (Grand Rapids, MI; Cambridge, U.K.: William B. Eerdmans Publishing Company, 2010), 135–136.

It is the Spirit who knows God’s thoughts (v. 11) and who was given to believers so that they might know the things God has freely given them (v. 12), things that can be known only by those who have the mind of Christ (v. 16). In light of the context and the use of the Greek verb in question, it seems Paul’s idea is that the Spirit serves as a special resource to believers, who may take their questions and concerns to God. The “spiritual person” is in a position to inquire into all things and find prophetic insight from God in connection with the wisdom of the cross.

Roy E. Ciampa and Brian S. Rosner, The First Letter to the Corinthians, The Pillar New Testament Commentary (Grand Rapids, MI; Cambridge, U.K.: William B. Eerdmans Publishing Company, 2010), 136.

Paul’s point: natural reason and intuition are completely unable to receive the divine realities unaided (contrast 1 Thess. 1:6, “you received the word with joy inspired by the Holy Spirit”; cf. 1 Cor. 2:13). Gaffin (1995: 114) cites Calvin’s caustic comments: “Faced with God’s revelation, the unbeliever is like an ass at a concert.” It is completely uninterested in the music and disturbs the concert with an irritating commotion. For example, the Athenian gadflies deemed Paul a “babbler” (Acts 17:18) and scoffed at his preaching of the resurrection (17:32). Gallio regarded the dispute between Paul and the Jews as silly talk (Acts 18:15), and Festus thought Paul to be insane (Acts 26:24). As Grindheim (2002: 697) observes, the “appropriation of divine wisdom requires a special ability. Natural human beings lack this ability (2:14), which is an exclusive attribute of the spirit of God (2:11b).”

Garland, David E.. 1 Corinthians (Baker Exegetical Commentary on the New Testament) (Kindle Locations 2759-2766). Baker Publishing Group. Kindle Edition.

to such a one that is folly, and he is unable to understand it, because it is spiritually discerned. Or, “that it is spiritually discerned,” because the force of hoti is not clear, whether it should be understood as causal (BDF §456.1) or as factual (BDF §456.2). To receive something from God’s Spirit would make no sense for the merely animated human being, who is incapable of grasping what can only be discerned in a spiritual way, i.e., guided by God’s Spirit. “Folly” is now taken up again, as an echo of 1:18, 21, “folly to those who are perishing.” In this context, that means that the psychikoi do not attain the knowledge required for salvation. Paul’s argument does not proceed from an analysis of human nature as such, but rather from humanity’s encounter with the revealed wisdom of God about what leads to salvation.

Joseph A. Fitzmyer, First Corinthians (The Anchor Yale Bible Commentaries) (Page 184).

This is even somewhat covered in my response to off-brand Leighton Flowers: