if state law were to have the higher power than federal law then the state's would be able to go against laws set by Congress with no repercussions. For example: during the 1950s Congress passed a federal law to end segregation. Arkansas tried to implement their own state laws to continue segregation in school. Of course it didn't work as Federal Law always reigns superior but if it was the other way around Arkansas would've had their schools segregated and the federal law could do nothing. I hope that helps.
