Each of the 12 steps has a spiritual principle behind it. The first 3 are:
Step 1 is Honesty
Step 2 is Hope
Step 3 is Faith
Since Step 4 asks for a "searching and fearless moral inventory of ourselves", COURAGE is the featured principle and feeling as you do a Step 4.
There are 3 main areas/feelings that people will address on a Step 4.
FEARS
RESENTMENTS
SEX HARMS
Honesty is also needed when doing a Step 4 to rid as much of the resentments and fears that can occupy the mind of an alcoholic and addict during the early part of their recovery.
Many in the program feel getting to and through a step 4 as quick as possible can be very beneficial in relieving the heavy weight of FEAR and RESENTMENT.
After this courageous and honest step, a person then releases this "inventory" to God and another person (a sponsor preferably).
The "work" starts at Step 4 and it can be difficult for some. But it also can release the burdens we carry around and prepares you for the rest of the Steps and your new life in sobriety.