Note 3 at Mt. 11:15: Everyone present probably had physical ears. Jesus is referring to their ability to perceive spiritual truth. Spiritual truths can only be received if we "incline our ear" unto God's Word (Prov. 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 towards those things (Ps. 92:6; Lk. 12:56; Jn. 8:43; 1 Cor. 2:14; Heb. 5:11).