يُولِجُ اللَّيْلَ فِي النَّهَارِ وَيُولِجُ النَّهَارَ فِي اللَّيْلِHe merges night into day, and merges day into night,meaning, He does what He wills with His creatures. He alternates the night and day and measures them by His wisdom, as He wills. Sometimes, He makes the night longer than the day, and sometimes the opposite. Sometimes, He makes the length of night and day equal. Sometimes, He makes the season winter, then changes it to spring, then summer then autumn. All this He does by His wisdom and His due measure of everything in His creation,وَهُوَ عَلِيمٌ بِذَاتِ الصُّدُورِand He has full knowledge of whatsoever is in the breasts.He knows the secrets, no matter how concealed they are