Bhashya
तथा विद्युति त्वचि हृदये च एका देवता; तेजस्वीति विशेषणम् ; तस्यास्तत्फलम्- तेजस्वी ह भवति तेजस्विनी हास्य प्रजा भवति- विद्युतां बहुत्वस्याङ्गीकरणात् आत्मनि प्रजायां च फलबाहुल्यम् ॥
In plain words
In the same way, within lightning, within the skin, and within the heart, there is one deity. 'Radiant' is its defining attribute. And this is the reward for realizing it: you become radiant, and your children become radiant. Because lightning naturally appears in many places, the fruit of this meditation multiplies across both yourself and your descendants.
Close to the Sanskrit
Likewise in lightning, in the skin, and in the heart, there is one deity; 'radiant' is the specific attribute. The fruit of that is: he becomes radiant, his offspring becomes radiant, -- because the multiplicity of lightning is accepted, there is an abundance of fruit in the self and in the progeny.