For a line outside a plane, as long as it's parallel to some line inside the plane, it's parallel to the whole plane.
Module goal. Master systematically the tests and properties of parallel lines, line-and-plane, and plane-and-plane, and learn to convert freely among them.
eastmath.com · 28.6 Parallelism in Space: Tests and Properties · 28.6.1 Test for a Line Parallel to a Plane