In "It Ain't Necessarily So," liable is shortened to li'ble in order to rhyme with Bible in the lines "Things you're li'ble / To read in a Bible," and - to some degree - this illustrates the speaker/singer's doubt. In the same way that liable lacks a syllable, the speaker/singer lacks complete faith.
None of the versions of "It Ain't Necessarily So" in my collection have the verses in the right chronological order. The Moody Blues' version has David, Moses, and then Jonah. In the Bible, Moses appears first ("found in a stream" in Exodus 2), then David (who "slew that Goliath" in 1 Samuel 17), and then Jonah (who "lived in a whale" in Jonah 1).
