Worship requires knowledge; good intentions are not enough. If good intentions were enough, then there would be no need for prophets to teach Islam. In fact, someone who commits a sin out of ignorance has two sins: one for committing it and one for not having learned. When society is full of such people it leads to disaster in this life and the next.

The Prophet said that seeking the knowledge of the Religion is obligatory on every Muslim (al-Bayhaqiy.)

Knowledge is Power, little knowledge can easily lead one to hell. The more you know, the better it is is for yourself. The least you know, you will never know if what you are doing will be accepted or not. As it says, intentions are not enough.

All the kufar who say we only ever do good, what use is that if it is not done for the pleasure of Allah in the correct way with the correct faith.

See the link as to what I mean by little knowledge can lead to Hell.
http://www.muftisays.com/blog/abu+mohammed/578_18-11-2010/who%27s-been-fooled.html