The peace of God (η ειρηνη του θεου). See in 2. Thessalonians 3:16 "the Lord of peace" (ο Κυριος της ειρηνης) and verse Philippians 4:9 for "the God of peace" (ο θεος της ειρηνης).

Shall guard (φρουρησε). "Shall garrison," future active indicative of φρουρεω, old verb from φρουρος (προ-οροσ, προοραω, to see before, to look out). See Acts 9:24; 2. Corinthians 11:32. God's peace as a sentinel mounts guard over our lives as Tennyson so beautifully pictures Love as doing.