Jesus says, "According to your faith let it be to you," similar to His words to the centurion whose servant was dying in Matthew 8:13. In both cases, the condition for the miraculous cure is faith. Faith opens the door for divine blessing; its lack closes the door. Christ could do few mighty works in Nazareth due to the people's lack of faith (Matthew 13:57-58). Similarly, salvation is a great work, but unbelief prevents it. It is important to study the Word of God to increase faith, as it comes by hearing or reading God's Word (Romans 10:17).
"Their eyes were opened" is more than a description of a literal action; it is also a Hebrew figure of speech. The Jews thought of blind eyes as "shut," and seeing eyes as "open." Jesus removes two men's blindness—they can now see and comprehend what was once closed to them. Thus, the opening of the eyes also suggests spiritual understanding.
Most people do not grasp the value or the meaning of Scripture, but Christ can open a person's eyes to enable him to understand His Word just as He did for His disciples after His resurrection (Luke 24:16-31, 45). The psalmist prays, "Open my eyes, that I may see wondrous things from Your law" (Psalm 119:18).