Were Paul's revelations ever revealed before in God's dealings with mankind?
No. The revelations given through Paul were never revealed previously in any of God's dealings with mankind. They were kept secret since the beginning of human history, or even before, and are not found in the Old Testament, Christ's earthly ministry, or the early parts of Acts.
Les teaches that these things coming from the epistles of Paul were never revealed previously in any of God's dealings with mankind. Many of Paul's doctrines cannot be found in the Old Testament, in Christ's earthly ministry, or in the early parts of Acts. They were revelations God had kept secret since the beginning of human history, or even before. Les also likes to begin with Deuteronomy 29:29, where the secret things belong unto the Lord our God, because He is sovereign and the Creator of everything. He suggests using a concordance to look up the word mystery wherever it appears in Paul's epistles and to study the concepts Paul associates with this revelation of a mystery.