Experiencing the Trinity

I highly recommend the book Experiencing the Trinity, by Darrell W. Johnson (associate professor of pastoral theology at Regent College in Vancouver, B.C.). Here is an excerpt from a review posted by the publisher:
To many people the Trinity is a puzzle that is difficult, if not impossible, to assemble. We are challenged to comprehend the “one is three and three is one”-ness of it. By exploring the relationships within the Trinity, we learn that God the Father, God the Son, and God the Spirit are truly one God and yet are, at the same time, three distinct Persons. It is through the relationship of the three that the distinctions are revealed. It is by this Triune-relationship God that we are created; it is for this Triune-relationship God that we were created.
Johnson writes of our inclusion in this Triune-relationship:
The moment we say "yes" to Jesus, we are welcomed into the eternal inner circle of love between the Father and the Son~love manifested in the Person of the Holy Spirit. In other words, we are welcomed “home” to an eternity filled with intimacy, joy, servanthood, purity, power, creativity, and peace.
In making his points, Johnson quotes frequently from C.S. Lewis and T.F. Torrance.  An exception I would take to what he says, is to state that when we say "yes" to Jesus, we are not included in the Triune life for the first time. Rather we are already included in that life and are now saying "yes" to actively participating in that which is already ours. We are now making "personal" and "realized," what has always been objectively true of us. Our acceptance of this truth does not create our inclusion, rather it helps us begin actively to participate and thus to enjoy what is already ours in Christ.

Johnson also writes about some of the ramifications of our inclusion in the triune life: 
A clear understanding of Trinity relationships affects our daily lives and our relationships. Since we were created in His image, what is true of the Father is true of us. In our daily lives this us-ness manifests itself in a number of ways:
- We need to be in relationship with others in order to be fully human.
- When relationships suffer, all of life suffers. We were created to need each other in righteous relationships.
- We need balance in our lives just as the Trinity relationships are in eternal balance. We must accept all three Persons of the Trinity into our lives to remain in balance.
- When we are baptized into the Trinitarian name, we are immersed into the relationship between God the Father, God the Son, and God the Spirit. It is possible to grasp this on an individual level.
- God will not rest until we truly experience the fullness of a Triune God on every level of our being.