When thou passest through the waters... — The two contrasted forms of elemental perils are used, as elsewhere, proverbially for all forms of danger (Psalms 66:12).
Related Commentaries of Isaiah 43:2
Isaiah 43:2
2 When thou passest through the waters, I will be with thee; and through the rivers, they shall not overflow thee: when thou walkest through the fire, thou shalt not be burned; neither shall the flame kindle upon thee.