From the datasheet...
Figure 3-3 shows the diagram for this pin. The GP3 pin
is configurable to function as one of the following:
• a general purpose input
• as Master Clear Reset
and...
bit 5 MCLRE: GP3/MCLR pin function select(5)
1 = GP3/MCLR pin function is MCLR
0 = GP3/MCLR pin function is digital I/O, MCLR internally tied to VDD
and from your config fuses...
_MCLRE_ON