Jonah contrasts the joy and comfort arising from the thought of God with the miserable fate of idolaters. They that observe (Psalms 31:6); court, pay deference to, reverence. Lying vanities; Septuagint, μάταια καὶ ψευδῆ, "vain things and false."
Idom (comp. Jeremiah 18:15; Hosea 12:11; 1 Corinthians 8:4). Their own mercy; i.e. their state of favour with God—the mercy shown to them, as "the mercies of [shown to] David" (Isaiah 55:3); or God himself, the Fountain of mercy and goodness (Psalms 144:2).
Henderson translates, "forsake their Benefactor."