What is the reason for the thinning (tarqiq) of the Glorious Name (Allah) in the verse: (Allah is the Eternal) if it is connected to the preceding verse (Say: He is Allah, the One and Only)?

The tanween noon at the end of the word (Ahadun) is saakin (vowel-less), and it was given a kasra (vowel-break) because it met with the saakin (vowel-less) lam of the majestic name (Allah). This kasra is the reason for the tarqeeq (lightening) of the lam of the majestic name (Allah) in this case, in accordance with the rule of vocalizing the first of two quiescent letters with a kasra when they meet.