Structural Functionalism is a Sociological Theory that tries to explain the reason why society works the way it does by studying the relationships between the many institutions that make society, such as family, religion, education, government, etc.
Modernization results in a shift of the responsibilities of each institution. In modern times, values and institutional structures are changing, and with them , their roles in society.
For example, Religion is playing a smaller role in society than it used to, and the principles and values that were to be implemented and/or passed by it, are now the responsibility of other institutions, for example. Some might even be lost and considered to be no longer important for society. That could be one of the results of modernization.