but Matthew has it in the shortest form (Mark precedes Isaiah with some words from Mal. 3:1, and Luke carries the Isaiah passage further).

Prepare may be used of making a thing ready or keeping it ready. Here the imagery is of a road that needs to be repaired so that it may be ready for the Lord to travel over it smoothly. Way may be used in the literal sense of a road; here the imagery is that of the road over which a king will approach.