What is the meaning of "ha'Lo Zos Ta'aseh Lach"?
Rashi: Your guilt and sin of abandoning Hashem caused this evil and punishment.
Why does it say "Ta'aseh" (feminine)?
Radak: It refers to "Azvech" (your abandoning, which is Makor, i.e. like an infinitive). Makor is like a noun; male and female apply to it. Below (verse 19 - "Ra v'Mar Azvech Azvech Es Hashem" it is masculine. The Makor "ha'Nekalah v'Einechem Hischaten ba'Melech" (Shmuel I, 18:23) is feminine.
What is the meaning of "b'Es Molichech ba'Darech"?
Rashi: When He was teaching to you the good, straight path. Radak - ba'Darech (with Patach under the Beis, in place of the prefix Hei) refers to a known way - the path of your first fathers. You veered from it, to go after other gods.
Malbim: This is a metaphor - like an orphan. His father was leading him on the road, and he abandoned him and strayed in the Midbar. The first to find him acquires him. So you were Hefker to be despoiled.
