Is Paul's sonship and heir teaching a one-off statement or consistent doctrine?

Paul's teaching on sonship and heirship is consistent doctrine, not a one-off statement. He says it over and over, making it part and parcel of Pauline doctrine. It fits everything else he wrote and is not a unique point in his writing.

Les teaches that Paul's sonship and heir teaching is not a slip of Paul's pen; Paul says it over and over, and it is part and parcel of Pauline doctrine. Les explains that it was not just a unique point in Paul's writing but fits everything else he wrote. He connects it to Romans 8:14, where those led by the Spirit of God are sons, and notes that if you are a son, you are an heir—a joint heir with God Himself. Les prefers using multiple Scripture portions, warning against building doctrine on only one or two verses.

Was Paul's statement about sons and heirs a one-time slip or a consistent doctrine?

Paul's sons-and-heirs teaching was not a one-time slip. He says it over and over, and it is part and parcel of Pauline doctrine. It was not a unique point in his writing; it fits everything else he wrote, including Romans 8:14, which addresses all led by the Spirit of God.