Matthew 13:15

For the heart of this people has become dull; they are hard of hearing, and they have shut their eyes, so that they would not see with their eyes and hear with their ears and understand with their hearts and turn, and I would heal them.’ ¹ 

Ps 119:70; Isa 29:10-12; Isa 44:20; Isa 57:18; Jer 3:22; Jer 17:14; Jer 33:6; Ho 14:4; Zec 7:11; Mal 4:2; Mr 4:12; Joh 8:43,44; Ac 3:19; Ac 7:57; 2Th 2:10,11; 2Ti 2:25,26; 2Ti 4:4; Heb 5:11; Heb 6:4-6; Re 22:2

¹ sn A quotation from Isa 6:9-10. Thus parables both conceal or reveal depending on whether one is open to hearing what they teach.