According to this law the ratio of emissive power to absorptive power is same for all surfaces at the same temperature and is equal to the emissive power of a perfectly balck body at that temperature.
Hence e1/a1 = e2/a2 = ….. (E/A) Perfectly balck bdoy
A = 1, i.e., e/a = E
( eλ/aλ)= (Eλ)black
Now since (eλ)black is constant at a given temperature, according to this law if a surface is a good absorber of a particular wavelength it is also a good emitter of that wavelength.
This in turn implies that a good absorber is a good emitter (or radiator)