What does “comparing spiritual things with spiritual” mean?
“Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God. Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual. But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.” — I Corinthians 2 : 12-14
Learning to “press toward the mark for the prize of the high calling of God in Christ Jesus” (Philippians 3:14) involves many revelations. One is making sure we are not setting material waymarks for our spiritual growth. Christ Jesus, himself, said, “For with what judgment ye judge, ye shall be judged: and with what measure ye mete, it shall be measured to you again.” (Matthew 7:2) Mary Baker Eddy wrote: “You render the divine law of healing obscure and void, when you weigh the human in the scale with the divine, or limit in any direction of thought the omnipresence and omnipotence of God.” (S&H, p. 445)
Even though we may be looking for healing or supply, which seem at first to be materially measured, it is really a matter of perspective. If our perception is hampered by the wrong thinking which is sin, then we will be tempted to compare spiritual things with material, and our “heart [will be] waxed gross, and [our] ears [will be dull of hearing, and [our] eyes [we] have closed.” But if we learn to apply right thinking, we will “see with [our] eyes and hear with [our] ears, and should understand with [our] heart, and should be converted, and [the Christ] should heal [us].” (Matthew 13:15)
The real healing we should strive for is that which enables us to move forward best expressing the qualities of Truth, Life, and Love in all we do; it's not getting back to one hundred percent, but realizing we can never be more or less than God made us to be. Similarly, the real supply we should seek is that which has never been absent from us, namely, the ability to be loving, kind, compassionate, honest, helpful, etc. Mrs. Eddy wrote: “God gives you His spiritual ideas, and in turn, they give you daily supplies. Never ask for tomorrow: it is enough that divine Love is an ever-present help; and if you wait, never doubting, you will have all you need every moment.” (Mis. p. 307)
In other words, when we “seek first the kingdom of God, and his righteousness” then “all these things shall be added unto you.” (Matthew 6:33) But if instead we seek either material ends through spiritual means, or spiritual ends through material means, then we forfeit both the healing and the supply which only come from seeking “first the kingdom of God.”