INFJ : Old Souls, Young Hearts

The Counselor, The Advocate, or The Harmonize-Seeking Idealist are characterized by a complex personality and an abundance of thoughts and feelings. They are warm-hearted persons by nature. They are sympathetic and understanding. Harmony-seeking Idealists expect a lot of themselves and of others. They have a strong understanding of human nature and are often very good judges of character. They have a lively fantasy, often an almost clairvoyant intuition and are often very creative. Once they have tackled a project, they do everything in their power to achieve their goals. In everyday life, they often prove to be excellent problem solvers. They like to get to the root of things and have a natural curiosity and a thirst for knowledge.
(source : http://www.ipersonic.com/type/HI.html#)

Beneath the quiet exterior, INFJs hold deep convictions about the weightier matters of life. Those who are activists -- INFJs gravitate toward such a role -- are there for the cause, not for personal glory or political power.

INFJs are champions of the oppressed and downtrodden. They often are found in the wake of an emergency, rescuing those who are in acute distress. INFJs may fantasize about getting revenge on those who victimize the defenseless. The concept of 'poetic justice' is appealing to the INFJ.

Writing, counseling, public service and even politics are areas where INFJs frequently find their niche.
(source : http://typelogic.com/infj.html)

INFJs tend to see helping others as their purpose in life, but while people with this personality type can be found engaging rescue efforts and doing charity work, their real passion is to get to the heart of the issue so that people need not be rescued at all.
"Help Me To Help You" is the point.
INFJs indeed share a very unique combination of traits: though soft-spoken, they have very strong opinions and will fight tirelessly for an idea they believe in. They are decisive and strong-willed, but will rarely use that energy for personal gain – INFJs will act with creativity, imagination, conviction and sensitivity not to create advantage, but to create balance.
(source : http://www.16personalities.com/infj-personality)