يَرِثُنِى وَيَرِثُ مِنْ ءَالِ يَعْقُوبَ ۖ وَٱجْعَلْهُ رَبِّ رَضِيًّا

This is the prayer of one who had grown very old while pursuing a religious mission and failed to find among his family members anybody to carry on his task after him. The feeling of his own helplessness on the one hand, and the realization of the tremendous importance of his mission on the other, combine in the prayer expressed in these verses. In other words, this was not a mere prayer for a son in the usual sense: it was a prayer for a worthy successor capable of carrying on his prophetic mission after him.

— Source: Tazkirul Quran (Maulana Wahiduddin Khan) via Quran.com (19:6)