What is the purpose of including sea level pressure and temperature in a METAR?
The sea level pressure allows pilots to calibrate their altimeters to make sure they are accurate. KGOK is 1069 feet elevation, if a pilot were to set their altimeter to 1020hpa (or 30.11 inches of mercury as used in the US, that's the A3011 in the METAR) then their altimeter would read 1069ft at ground level.