Our hearts can become dull of hearing, when the Word of God that should produce faith in us does not penetrate into our ears for us to hear or into our eyes for us to see. When we are dull of hearing the question is, does the Word of God become of non-effect? Well Jesus said that the hearing of His word causes one to turn and come to Him with the result of being healed. The word has gone out, ‘Behold I make all things new’. The old does not hear clearly but the New does hear clearly. Though we may not hear as clearly as we might, we need to persist keeping the Words of God in our mouth, because that which is coming out of our mouth will cause us to turn in that direction. The new is there to behold and to rest in, one must keep knocking until the door is open to walk into it.
https://biblehub.com/matthew/13-15.htm