A puja is a ceremony in which prayers are offered to the Buddhas to request their blessings or invoke their help. Pujas are performed to avert and clear the three types of obstacles, conditions which prevent us from achieving our worldly and spiritual goals. 

» There are three types of obstacles:

1. Worldly obstacles
these are affecting day to day life, relationships, business, finances. 

2. Inner obstacles
They affect our health or mental state.

3. Secret obstacles
Obstructing the attainment of innate wisdom. 
By making extensive prayers and offerings with sincere motivation, unfavorable circumstances that bring problems can be changed. It is said that prayers performed by ordained ones are especially powerful and effective as they are done on the base of pure morality.
Similarly making offering to the assembled Sangha during a puja collects extensive merit and purifies obstacles.

» Pujas can be performed for various purposes:

1. for the dying
to help pacify their mind, and decrease fear during the time of death.

2. for the deceased
to bless and guide their mind to a higher state of rebirth and liberation. 

3. for sickness
to remove obstacles to mental and physical health. 

4. for success in one's activities
removing obstacles to success of one's activities, be they worldly or dharma.

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The puja performed depends on the type of problem and the individual's karma. Usually a lama is consulted for advice on the type of puja (divination).