Look to some of the leaders of the past.
It doesn't seem that John Bunyan had much of an education. He was the son of a tinker. Leaving that he joined the army. After the army he led, for a time, a rather care-free life until he got married. His wife had only two books. One biographer says that he had to learn again how to read. That was in 1648, following a spiritual battle which lasted four years.
John Gifford helped him find that peace, probably around 1652. He joined his church in 1653, was baptized in 1655 and began to preach in 1656.
In 1658 he was indicted though not yet jailed.
In 1660 he was jailed for the next 12 years for preaching without a licence.
He had little education but was a powerful preacher. Now he had two books--the Bible and Foxe's Book of Martyrs. During this time he wrote "Pilgrim's Progress," which for many years was the worlds best selling book, next to the Bible.
For all intents and purposes the only resource that Bunyan ever had was the Bible. He didn't have much access to anything else. That is why he was such a great preacher. Prayer plus Bible.