“took her prostitution lightly.” The Hebrew is more literally, “the lightness of her prostitution,” but we would express that as she “took it lightly” or in other words, “it mattered very little to her.” Judah was like Israel in that her idolatry and sexual sin mattered little to her, and just as Israel was deported to Assyria, eventually Judah was deported to Babylon, and even after Judah was allowed to return to their homeland during the Persian empire, after they were deported to Babylon there never has been a time when there were as many Jews in Israel as there were scattered abroad. Sadly, much of the modern world is in the same position today. Israel and Judah experienced ruin from Yahweh because they abandoned Him, and people today can expect the same thing.
“stones and with trees.” The pagan idols were made of stone and wood. People today have to be cautious about the same thing. It is easy to make something made of rock (or minerals) or wood or other materials into an idol. People who have a “lucky hat” have an idol made of cloth; and people who think that plastic prayer hands on the dashboard of a car keeps them from being in a wreck also have an idol. Spiritual help comes from God, and if we want His blessing we live godly lives and pray hard. It is fine to have objects that remind us of God or remind us to pray, but we are never to think that spiritual help comes because of the object. Never rely on wood and stone for any help—it is an offence to the One who created those materials.
God says that when you turn to wood and stone objects for help you are committing adultery with them. God is to be our Lover, and when we forsake Him, no matter how innocently or ignorantly, and turn to other things for spiritual help, it hurts Him and affects the blessings we receive from Him.