I think you are asking why Earth gets the most effective heat from the Sun for life. Earth happens to contain several features that make it ideal for habitation with organic life forms. Perhaps most importantly, it is the ideal distance from the Sun to receive the optimal level of its radiation. Between the Sun's radiation and the natural heat produced in the core mainly through radioactivity, we get a range of temperatures very conducive to organic life. Liquid water is also able to abundantly exist, and the atmosphere keeps enough of the heat trapped at night to prevent excessively cold temperatures. Mercury and Venus are too close to the sun to allow for liquid water (too hot), and all of the planets further than Mars are too far away from the Sun and too cold. So really it is the distance from the Sun that happens to make Earth the ideal planet for life as we know it.