Note 3 at Mt 11:15: Everyone present probably had physical ears. Jesus was referring to their ability to perceive spiritual truth. Spiritual truths can only be received if we incline our ears unto God's Word (Pr 4:20). What we concentrate our attention upon is what we become sensitive to. If we fail to meditate upon spiritual realities, we will become dull of hearing (spiritually) or hardened toward those things (see note 10 at Mr 6:52; also see Ps 92:6, Lu 12:56, Joh 8:43, 1Co 2:14, and Heb 5:11).