Mat 15:14 Let them alone: they be blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch.

On the surface, this is just good advice about following those who do not understand where they are. However, symbolically, Christ is tying together two fundamental ideas.

Sight is Christ's symbol for understanding physical reality. There is a distinct different in Christ's teaching between misunderstanding the physical world and misunderstanding the mental world. Physical reality is more obvious. It is something that a child can simply see. Therefore Christ uses the metaphor of blindness as the absence of this understanding rather than ignorance, which indicates a lack of mental knowledge.

The earth is Christ's symbol for relationships. caring, and the heart. Here, we the pit is the absence of earth, literally, a hole in the heart. Christ is saying that those who don't understand physical reality naturally lead to mistakes in their relationships with people. This is actually an attack on those (unfortunately, like me) who live too much in their heads and not enough in the physcial world of real relationships.

Symbolic translation: Leave them alone, without understanding reality, they guide others who don't also understand reality. If the insenstive lead the insenstive, they fall into hole in their heart.

"Let alone" is from aphiêmi, which means to primarily "to send forth" and "discharge," but the word almost as often translated in the NT as either "leave" or "forgive." It use here with autos, (reflexive pronoun, here, "themselves") it tends to mean "leave them to themselves."

"Blind" is from tuphlos, which means "blind," but which is also a metaphor for disabilities of the other senses.

"Leaders" is from hodêgos, which means "guide." "Lead" is from the verb form, hodêgeô, which means "to lead upon the way." These concepts were also used for those who helped those ignorant of a given area.

"Ditch" is from bothunos, a form of bothros, which means any hole or pit dug into the earth.