By pureness, by knowledge, by longsuffering, by kindness, by the Holy Ghost, by love unfeigned,
By ... by ... - Greek, 'In ... in,' etc.; not the instrument, but the sphere or element in which his ministry moved.
Knowledge - spiritual; in Gospel mysteries, unattainable by reason (1 Corinthians 2:6-16; 2 Corinthians 3:17-18).
Long-suffering ... kindness - associated with "charity" or "love" (1 Corinthians 13:4), as here.
By (Greek, 'in') the Holy Spirit - in virtue of His influences which produce these graces "love unfeigned" being the foremost.