A mustard seed is a very small seed. Jesus implies that they do not have even a small amount of faith. Alternate translation: "If you had faith that was even as small as a mustard seed, you" or "Your faith is not as big as a mustard seed—but if it were, you" (See: [[rc://en/ta/man/translate/figs-simile]] and [[rc://en/ta/man/translate/figs-explicit]])
If this type of tree is not familiar, it may be helpful to substitute another type of tree. Alternate translation: "fig tree" or "tree" (See: [[rc://en/ta/man/translate/translate-unknown]])
These can be stated in active form. Alternate translation: "Uproot yourself and plant yourself in the sea" or "Take your roots out of the ground, and put your roots down into the ocean" (See: [[rc://en/ta/man/translate/figs-activepassive]])