here's how i teach it to 6 year olds, 16 year olds and adults:
the blessed trinity is the central mystery of our faith.
central means it is the heart of everything we belive.
mystery meands there is MUCH we can know about this but not everything. and there is MUCH we can undeerstand about this but not all-- and not ever. it is only completely knowable and understandable to the mind of God.
but because God HAS revealed this, we believe it.
here's how it goes. there is ONE God in three divine persons-- the Father, Son and Holy Spirit. they each completely share the essense ogf God, but they are three persons of one essence. three PERSONS, means they each have a relationship with each other-- a perfect relationship of eternal love. and one essence-- which is God. if it coyld be divided or reduced, it would not be God. but the essence is complete in each person, shared completely by each divine person.
when you were baptized, you were baptized into the mystertious life of the Blessed Trinity== the mysterious life of God.
the illustration below is o so cool. that's how i teach it.
here's why the egg, grandmother and steam analogies dont work. st patricks is lacking too-- and it MUST be lacking if it is truly mystery-- no one can explain it filly.
but the egg analogy fails in this: the shell, youlk and white are all parts of the egg. each is not complete egg. but Father, son and spirit are each completely God.
the steam doesnt work, because the Father doesnt morph intot he Son or the Spirit. they are separate persons.
the mother-daughter - grandmother analogy probably fails most of all-- because as moither, wife and daughter, i am three ROLES, but one person. if mother me spoke to wife me and loved daughter me as a seperate entity, it would be a sign of mental illness.
one of the most astonishing clues about the TRI-UNITY of the trinity is found in gospel matthew 28:19, "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,"
Jesus told them to baptize in ther NAME of, though he named THREE.
until the Holy Spirit descended on pentecost, the apostles didnt know how that single NAME could be the NAME of three.
best treatment: Frank Sheed's Beginning Theology. excellent read!!!!!!!!!!!!!!