The reasons for wanting to twin are many and varied. 
Different sources refer to:

-  the universality of the church
 - the Vatican II definition of “mission"
- expansion of a parish self-identity
 - response to Jesus' call to Justice in scripture
 - solidarity with the poor

For one pastor's "take" on Twinning and why it is important, see Fr. Al Hurt's homily from our October 2005 Twinning Celebration Mass and Gathering at St. Monica, St. George Parish in Clifton. Click here for the text.

To gain an in-depth understanding of the “whys” of twinning, please refer to the following resources/links that have expanded on the topic.

Applicable Resources/Links:
“Building Friendships and Solidarity in Christ Across Cultures” see page 2
"The Why’s of Twinning"  Fr. Bill Nordenbrock, CPPS
“Four Stages of Spiritual Growth in Helping the Poor” Fr. Albert Nolan, OP
"Why Catholic's Should Hang Out with the Poor" Sr. Helen Prejean, CSJ