Subdividing list with another list as a reference
Subdivide @@@ Partition[Flatten@Riffle[Partition[list1, 2, 1], div], 3]
or
Subdivide @@@ Flatten /@ Transpose[{Partition[list1, 2, 1], div}]
or
Subdivide @@@ Transpose@{list1[[;; -2]], list1[[2 ;;]], div}
or
Subdivide @@@ Transpose@{Most@list1, Rest@list1, div}
Can it be done shorter....
Another way:
MapThread[Subdivide, {Most@list1, Rest@list1, div}]
The answer you want can be reached this way:
list1=Partition[list1,2,1]
f=MapThread[Insert,{list1,div,Table[3,{Length[list1]}]}];
Apply[Subdivide,f[[#]]]&/@Range[Length[list1]]