The expression 'by the Spirit' occurs in vers. 18 and 25; but in ver. 16 'walk' refers to the general manner of life, as Rom. 8.4, so I have left 'in.' In vers. 18 and 25 'walk' refers to the rule or line followed, as ch. 6.16; Rom. 4.12; Phil. 3.16. It is characteristic of the walk, leading, and life, the Spirit being the instrument and power.