The man's deafness was absolute; he could hear nothing. This greatly limited him, especially in those days when sign language and other communication helps did not exist as prominently as they do today. The poor had no access to speech therapists, and the medical practices of the time offered no hope at all.
His deafness also put him in danger, as people use their hearing more than they realize to avoid harm. Spiritual deafness is no different: When we cannot hear or refuse to hear the Word of God, we endanger ourselves greatly, not hearing the warnings of God's ministers against the enticement and pull of sin and its curses and penalties. While physical deafness is a very limiting disability, it does not normally lead to death, but spiritual deafness is infinitely worse, leading to eternal death.
The man was almost entirely mute except for a speech impediment that kept him from communicating with others verbally. The word "impediment" in Mark 7:32 does not mean he could not make any sounds but that he had great difficulty in speaking. He could make sounds with his mouth, but they came across as gibberish. Mark's account states that Jesus "loosed" the man's tongue, which may indicate that the problem was a birth defect.
Deafness and dumbness are often associated because humans learn to speak by hearing. A person who cannot hear his own voice or the voices of others has difficulty with pronunciation. If a person becomes deaf later in life, he will be able to speak much better than one born deaf or who loses his hearing as a child.
The relationship between the inability to speak and deafness pictures some of sin's effects. Those who are deaf to the Word of God will have great difficulty speaking properly of spiritual matters. Even the most educated sinner betrays an impediment in his speech as soon as spiritual truths are introduced, but when he opens his ears to receive the truth, his spiritual speech will improve greatly and continually. Just as Jesus physically healed the man to enable him to hear, He must spiritually heal us so that we can understand God's Word (see John 8:47; I Corinthians 2:9-14).
Martin G. Collins
The Miracles of Jesus Christ: Healing a Deaf-Mute (Part One)