Literary: The literary expectation of the "all sorts" of fruit being good extends through verse 31, with the anti-climax occurring in 32. As a literate piece, this is a nice tension where the expectation of success is forcibly (and with somewhat dramatic sadness) reversed. The visually promising fruit is not as good as the promise. The Lord declares that "it profiteth me nothing." As a botanical reference, this would be a fruit incapable of producing salable oil. In a spiritual sense, the promise is there, but the various forms of godliness are incapable of the exaltation of the soul of man. While there may be other uses for such fruit, for the desired and ultimate goal, they "profit nothing."