Charles Ellicott Commentary Isaiah 43:2

"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." — Isaiah 43:2 (ASV)

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).