Jamieson, Fausset and Brown on Hebrews 10:39

39. A Pauline elegant turning-off from denunciatory warnings to charitable hopes of his readers (Ro 8:12).

saving of the soul--literally, "acquisition (or obtaining) of the soul." The kindred Greek verb is applied to Christ's acquiring the Church as the purchase of His blood (Ac 20:28). If we acquire or obtain our soul's salvation, it is through Him who has obtained it for us by His bloodshedding. "The unbelieving man loses his soul: for not being God's, neither is he his own [compare Mt 16:26, with Lu 9:25]: faith saves the soul by linking it to God" [Delitzsch in Alford].