Why did Alexander II sign the Act of Emancipation?

The Act of Emancipation of 1861 is considered one of the best laws in history. Alexander II wanted to free the serfs (people who required services towards lords, etc). He realized than freeing more than 40 million serfs was not going to be an easy task, so he created the law that stated serfs can marry, own their own property, and argue in court cases. Also, the owners of the property that the serfs worked on, the owners had to now pay the serfs for their work.