You could use the (array:) macro to create a collection of Passage names, then use the (shuffled:) macro to randomly sort those names, and finally a (link-goto:) macro to create the link using the 1st element in the shuffled array as the name of the Target Passage.
(set: _list to (array: "Passage 1", "Passage 2", "Passage 3", "Passage 4", "Passage 5", "Passage 6"))
(link-goto: "Next", (shuffled: ..._list)'s 1st)
... obviously your Passage names would be more meaningful than the ones in the above example.
note: You don't state what type of value is stored within your "six variables" but if you really need to use there value as the determining factor and if those six variables contain the Passage names then you could build the Array of Names using them like so.
(set: $passageA to "Passage 1")
(set: $passageB to "Passage 2")
(set: $passageC to "Passage 3")
(set: $passageD to "Passage 4")
(set: $passageE to "Passage 5")
(set: $passageF to "Passage 6")
(set: _list to (array: $passageA, $passageB, $passageC, $passageD, $passageE, $passageF))
... and then use the same (link-goto:) macro as the first example.