We have become such experts, as we think, in psychological understanding, and at dividing people up into groups–psychological, cultural, national, etc.–that we conclude as a result that what is all right for one is not right for another, and so eventually become guilty of denying the Gospel. ‘There is neither Jew nor Gentile, Barbarian, Scythian, bond nor free.’ This is the ONE Gospel–the ONLY Gospel. It is for the whole world, and the whole of humanity. Mankind is one. We have fallen into the grievous error of adopting modern psychological theories to such an extent that we evade the truth, sometimes to protect ourselves from the message, and certainly often to justify methods that are not consistent and consonant with the message which we are privileged to deliver.
Preaching & Preachers (Grand Rapids, MI; Zondervan; 1972) p. 141-142