"Which things we speak." "Which things" means what we know through the Spirit whom we have received from God: all the mysteries of the Kingdom and the whole divine economy of salvation.
"We speak" means we preach and proclaim to all. "Not in words taught by human wisdom" means not in the verbal form devised by human wisdom for handing its teaching on to others.
The thought here is the same as in the words, "not in persuasive words of human wisdom," or, "not in wisdom of speech." Every verbal art taught by rhetoricians is denied.
The essence of this art is to stir the movements and passions of the heart by various turns and devices of speech. Through this it takes possession of minds and inclines them to its side.
Since everything passionate can be turned only toward the earthly, worldly, and fleshly, and the wisdom of God belongs to the opposite realm, the Spirit did not accept devices of speech invented to stir passions.
He did not accept them when He imparted the wisdom of God to men. We, he says, did not use them either.
We had our own methods. As the Spirit of God taught, so we spoke. The Spirit of God inspired definite truths. They called forth definite concepts, and the concepts drew definite words to themselves.
These words were taken from the sum of words possessed by the one to whom the truth was revealed. Likewise the manner of speech awakened was the one to which the receiver of revelation was accustomed or akin.
Yet when it was necessary to offer the teaching, he did not go to rhetoric for art. He did not even concern himself with the word.
It flowed from the heart, set in motion by the Spirit, who impressed there the mysteries of the Kingdom. The Apostle expressed this when he said, "we speak in words taught by the Holy Spirit."
The Lord also promised the same when He said, "Do not worry how or what you should speak, for it will be given you in that hour what you should speak. For it is not you who speak, but the Spirit of your Father who speaks in you" (Mt 10:19-20).
"Comparing spiritual things with spiritual." "Comparing" is συγκρίνοντες. This verb means fitting one thing to another so that they correspond to each other.
"Spiritual things" means the wisdom of God and all the truths inspired by the Spirit of God. "With spiritual" means with spiritual words, turns of speech, and ways of expressing the revealed truths.
Thus the Apostle says: for spiritual truths we choose words and turns of speech corresponding to those realities. These also must be called spiritual.
We never allowed ourselves to descend from the height on which contemplation, wrought by the Spirit of God, placed us. We did not seek ways of expressing divine truths here, in the sphere of vain human wisdom.
Although the Spirit of God moved the tongue of the evangelists, they did not lose self-possession. They directed their speech consciously.
Chrysostom explains where the necessary things for clarification are taken from. He says they are taken from types and prophecies.
Here are his words: "What does 'comparing spiritual things with spiritual' mean? If some difficulty arises concerning a spiritual matter, we bring explanations from spiritual things."
"For example, I say that Christ rose and that He was born of a Virgin. For explanation I bring testimonies and types. Jonah's stay within the whale and his subsequent deliverance from it are such a type."
"So also are the births of barren women, Sarah, Rebecca, and others. So also is the growth of trees in Paradise when no seeds had yet been cast, no rain had fallen, and no furrows had been drawn."
"For future events were traced and prefigured by earlier ones, as in a shadow, so that men might believe them when they came to pass."
"I also show how man came from the earth, how without any union woman came from one man, how the earth itself came from nothing, and how everywhere and in everything the Creator's power was sufficient."
"Thus I explain the spiritual by the spiritual, and nowhere do I resort to external wisdom, to reasonings and inferences."
"The wise men of the Gentiles strain and torment their weak reason, yet they cannot explain what they speak about. They even do the opposite. They bring greater confusion and increase darkness and perplexity."
So also teach all our interpreters: Theodoret, Oecumenius, and Theophylact. Among other things, Theophylact also expressed this thought.
"Comparing spiritual things with spiritual" means offering spiritual truths to spiritual persons, or discussing spiritual matters with spiritual persons. For such persons alone can contain them.
Πνευματικὰ πνευματικοῖς συγκρίνοντες. Πνευματικοῖς may also be translated as a dative. Some newer interpreters have followed this and have formed the opinion that this is precisely what the Apostle wished to say here.
To prefer this opinion to the first would perhaps be excessive. Yet it should not be entirely despised.
The following text gives it probability: "But the natural man does not receive the things of the Spirit of God." It seems to be called forth by what has just been said.
That is, we strive to present spiritual things to spiritual persons, or to discuss spiritual matters with spiritual persons. They alone are able to receive them. But the natural man does not receive the spiritual.
The implication is that we do not even offer it to him. So also the Savior commanded us not to cast pearls.