1) When Christians tried preaching in India, they were surprised to see Mr. M. K. Gandhi, leader of the freedom struggle, already practicing the very essence of Bible.
2) Swami Vivekananda (the Star Campaigner of Hinduism) got a shock of his life when he met a Christian boy already practicing the very essence of Hinduism when he was on a foreign tour. Vivekananda purchased one kilogram of apple from a shop and started walking with it. A boy who was following him stopped him and wanted to repurchase the apple, offering the double amount. When asked why, boy replied: “I saw the shopkeeper mixing spoiled apples also when you were busy talking to other customers. When you return to your country, I don’t want you to speak ill of our country.” Vivekananda promised he would not speak ill of his country because of the loft attitude the boy manifested. But he understood even little ones are endowed with moral sense which means preaching is not needed.
3) People are able to do what is right if they want to, hence Jesus declared that some chose to do what is good and others choose to do what is bad. (Mathew 12:35) Preaching would often not make any difference. (Revelation 22:11) This is why Jesus himself declared categorically that no preaching work is God-ordained. (Mathew 7:21-23) Learning from experience (own or of others) is the mechanism God has put in place. (Luke 6:38) This would either result in upward evolution of mankind or their downward evolution (in which case God can always “renew” what has become decadent.—Mathew 19:28)
This means all preaching references found in the Bible are later adoptions.