Where can I read the oldest and purest texts of Buddhism?

I happen to read this text from the _Buddhist Catechism_ (which was written by Olcott, published 1881): > Q. What striking contrasts are there between Buddhism and what may be properly called "religions?" > > A. Among others, these: It teaches the highest goodness without a creating God; a continuity of life without adhering to the superstitious and selfish doctrine of an eternal, metaphysical soul-substance that goes out of the body; a happiness without an objective heaven; a method of salvation without a vicarious Savior; redemption by oneself as the Redeemer, and without rites, prayers, penances, priests or intercessory saints; and a summun bonum, i.e., Nirvâṇa, attainable in this life and in this world by leading a pure, unselfish life of wisdom and compassion to all beings. But any recent texts I read about Buddhism all make it appear as if Buddhism is no different from any other dogmatic religion. I understand that Buddhism also underwent a lot of changes due to local cultures and competition from other religions. What I want to learn is the original core message of Buddhism before it was made into a religion. Where can I find texts for understand this message.