By the word of truth, by the power of God, by the armour of righteousness on the right hand and on the left,
By the word of truth, by the power of God - rather, 'IN ... in,' etc. As to "the word of truth," cf. 2 Corinthians 4:2; Colossians 1:5, and "the (miraculous) power of God," 1 Corinthians 2:4; 2 Corinthians 4:7.
By the armour, х dia (G1223)] - 'through,' or, 'by means of the armour,' etc.
Righteousness - only the breastplate in Ephesians 6:13-17; here is the whole Christian panoply (cf. 2 Corinthians 10:4).
On the right hand and on the left - offensive weapons for the right hand, defensive for the left. He could, in conscious integrity, attack the bad as well as defend himself from them.