The word "ineffable" refers to something that is impossible to express or describe using words. It describes experiences or feelings that are so intense, beautiful, or overwhelming that they cannot be adequately put into words. Full definition
Because good and holy liturgy lifts up our hearts — sursum corda, as the Roman Canon reads — to an experience of transcendent and ineffable mysteries. (firstthings.com)
«Peace» is experienced as ineffable unity and harmony, yet is only partially grasped and understood. (religion-online.org)