The helmet of salvation (tēn perikephalaian tou sōtēriou). Late word (peri, kephalē, head, around the head), in Polybius, lxx, 1Th 5:8; Eph 6:17 alone in N.T.
Which is the word of God (ho estin to rēma tou theou). Explanatory relative (ho) referring to the sword (machairan). The sword given by the Spirit to be wielded as offensive weapon (the others defensive) by the Christian is the word of God. See note on Heb 4:12 where the word of God is called “sharper than any two-edged sword.”