(… ذَٰلِكَ مِنْ أَنبَاءِ الْغَيْبِ ) (That is from the news of the unseen which We reveal to you, [O Muhammad]…): It’s unseen by Prophet Muhammad (saws) but known to him because it had happened. This is an unseen history, and is more credible than what is sensed since it’s told by the Almighty.
(… نُوحِيهِ إِلَيْكَ …) (…We reveal to you, [O Muhammad].…): It’s all -the talk about Virgin Mary who was chosen above the women of the worlds and the introduction to the great even of the birth of Jesus Christ along with what happened with Zechariah and naming John (PBUT)- revealed to you (Prophet Muhammad).
(… وَمَا كُنتَ لَدَيْهِمْ إِذْ يُلْقُونَ أَقْلَامَهُمْ أَيُّهُمْ يَكْفُلُ مَرْيَمَ …) (…And you were not with them when they cast their pens as to which of them should be responsible for Mary …): There was a dispute between Zecharia (PBUH) and his people as they all wanted to care for baby Mary, and they casted lots by the pens they used to write the Torah with so that whoever gets the vote cares for Mary. Consequently, Zechariah (PBUH) was chosen.