A "mustard seed" is a very small seed. Jesus implies that they did not have even a small amount of faith. AT: "If you had faith that was even as small as a mustard seed" or "If only your faith was as big as a mustard seed, but it is not" (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. AT: "a fig tree" or "a tree" (See: [[rc://en/ta/man/translate/translate-unknown]])
These can be stated in active form. AT: "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]])