FPGA elements complexity
A configurable logic block (CLB) has the capability to make itself a lookup
table, as well as other things. That's  why its a configurable. Logic. Block.
A hard core is a real processor in etched in silicon , inside the FPGA; The same
kind you might find in a standalone chip. 
CLBs make up the logic fabric in FPGAs while macrocells make up the fabric of CPLDs. Do you know the difference in functionality between a CPLD and FPGA?