That is certainly going beyond what is said in the text. It specifically
says the person without the Spirit. That is not immature Christians.
It is not any Christian at all.
6 However,
we speak wisdom among those who are mature, yet not the wisdom of this age, nor of the rulers of this age, who are coming to nothing.
7 But
we speak the wisdom of God in a mystery, the hidden wisdom which God ordained before the ages for our glory,
8 which none of the rulers of this age knew; for had they known, they would not have crucified the Lord of glory.
9 But as it is written: "
Eye has not seen, nor ear heard, Nor have entered into the heart of man The things which God has prepared for those who love Him."
10 But
God has revealed them to us through His Spirit. For the Spirit searches all things, yes, the deep things of God.
11 For what man knows the things of a man except the spirit of the man which is in him? Even so no one knows the things of God except the Spirit of God.
12 Now we have received, not the spirit of the world, but the Spirit who is from God,
that we might know the things that have been freely given to us by God.
13
These things we also speak, not in words which man's wisdom teaches but which the Holy Spirit teaches, comparing spiritual things with spiritual.
14 But
the natural man does not receive the things of the Spirit of God, for they are foolishness to him; nor can he know them, because they are spiritually discerned.
15 But
he who is spiritual judges all things, yet he himself is rightly judged by no one.
16 For "who has known the mind of the LORD that he may instruct Him?" But
we have the mind of Christ.
NKJ 1 Corinthians 3:1 And
I, brethren, could not speak to you as to spiritual people but as to carnal, as to babes in Christ.
2
I fed you with milk and not with solid food; for
until now you were not able to receive it, and
even now you are still not able;
3 for
you are still carnal. For where there are envy, strife, and divisions among you, are you not carnal and behaving like mere men?
(1 Cor. 2:6-3:3 NKJ)
This is not speaking of the foundational Gospel. It is speaking of the deep things of/from God that even "babes in Christs" - milk drinkers - cannot even be taught yet. Deep things from God concerning the things God has prepared for those who love Him. The things God had freely given to those who love Him.
The natural man has yet to even believe in Jesus Christ, so he has no chance of receiving/knowing them.
They are known only by mature Christians. When Paul says "spiritual" he's speaking of these mature Christians. It's not just that they have the Spirit, but are mature in Christ in Spirit. The babes in Christ are not yet Spiritual even though they are in Spirit. They're still drinking milk and acting fleshly.