I missed the end of the film, I know what eventually happened but I can't figure out how Matt got Richard to drive up into the woods.
shareIn addition to holding him at gunpoint, Matt convinced Richard that he was forcing him to flee the state and jump bail. He instructed Richard to pack clothes for warm weather, and explained to him that he wanted Richard far away and out of their lives. Of course, this was a complete lie that he was telling Richard to keep him cooperative, tricking him into believing that he was going to survive the encounter. What Matt really wanted was to make it appear to the authorities that Richard had simply packed up a few suitcases and skipped bail (note that before leaving Richard's house, Matt places a train ticket envelope in plain view on a table).
He then got Richard to drive into the woods by claiming that he was taking him somewhere to stay for a few days before boarding a plane.