A line passes through $(1, 0, 2)$ with direction ratios $(2, 1, -1)$. A second line passes through $(0, 2, 1)$ with direction ratios $(1, -1, 3)$. What is the value of $(\vec{a}_2 - \vec{a}_1) \cdot (\vec{b}_1 \times \vec{b}_2)$, and what does it show?