"'Your wickedness will punish you; your backsliding will rebuke you. Consider then and realize how evil and bitter it is for you when you forsake the Lord your God and have no awe of me,' declares the Lord, the Lord Almighty." NIV translation
God basically tells His people to look at their surroundings and to realize that their current condition is because of their turning away from him. The same is true for us as well in that, if we find ourselves in a mess, we need to stop and search our hearts for sin. Although Jesus has paid for all our sins so that we are saved, we still suffer effects (consequences) of sin.
"'Long ago you broke off your yoke and tore off your bonds; you said, "I will not serve you!" Indeed, on every high hill and under every spreading tree you lay down as a prostitute.'" NIV translation
The people had decided that they could just go anywhere and worship God but He had commanded them to go to Jerusalem. They went to all of the hills and set up altars for worship but it was not what God desired from them. Although, today, we can worship God anywhere and at any time, the best act of worship is obedience. If we pursue the things of this world and the ways of this world instead of listening to God through the Holy Spirit, we too become like prostitutes and God is not happy with us either.
"'I had planted you like a choice vine of sound and reliable stock. How then did you turn against me into a corrupt, wild vine?'" NIV translation
The difference between a wild vine and one that has been planted and tended is in the fruit. With a vine that is planted and tended, you know what type of fruit will be produced and you know that it is good. With a wild vine, the wind can carry pollen and the fruit of the vine can be changed. Therefore, you cannot be sure of the quality of the fruit. God is telling His people that they chose to move away from Him (become wild) and so they are corrupted (you cannot be sure of the fruit). The same principle is true for us today in that, when we stay close to God by listening to the Holy Spirit, the fruit is good but, when we move away and try to do things on our own, the fruit can be corrupted.
"'Although you wash yourself with soda and use an abundance of soap, the stain of your guilt is still before me,' declares the Sovereign Lord." NIV translation
God tells His people that, no matter how hard they try, they cannot remove the memory of their sin from the mind of God. This passage reminds us of the hopeless state that the world was in before Jesus Christ. Through God's grace, our sins are paid for and we are as if they never even happened thanks to Jesus paying the penalty. As this verse says, we couldn't do it on our own.