Sincerity

"I know, my God, that you test the heart and have pleasure in uprightness." 1 Chronicles 29:17

God tests the heart. Those who are sincere please Him and are honored by Him. The rest are despised.

Flesh and Spirit

"For they that are after the flesh mind the things of the flesh; but they that are after the Spirit the things of the Spirit." Romans 8:5

To be after the flesh means submitting to the whims of the heart. It is impossible to succumb to your heart's desire and do the will of God at the same time. To be after the Spirit means submitting to His command, according to His Word.