Radak: Before I will return you to Me, you must know your sin and recognize why I exiled you - you rebelled against Me! Once you recognize this, return to Me and I will return to you.

Malbim: Know that your sin is three-fold. (a) You rebelled against Hashem Elokecha. (b) You were Hefker to all strangers, and everywhere, under every fresh tree. (c) I called to you to return to Me, and you did not heed Me.

Rashi: You rebelled.

Rashi: This is an expression of spreading the legs to be Mezanah with a woman.

Radak: You did not serve only one idolatry. You spread your ways to many - "Ki Mispar Arecha Hayu Elohecha Yehudah" (2:28).

Radak: I warned you constantly via Nevi'im, and you did not heed them.