﴿ فَٱتَّخَذَتْ مِن دُونِهِمْ حِجَابًۭا فَأَرْسَلْنَآ إِلَيْهَا رُوحَنَا فَتَمَثَّلَ لَهَا بَشَرًۭا سَوِيًّۭا ﴾

“and kept herself in seclusion from them, whereupon We sent unto her Our angel of revelation, who appeared to her in the shape of a well-made human being.”

(And had chosen seclusion from them) so that she purifies herself after the end of her menses. (Then We sent unto her Our Spirit) Our Messenger Gabriel when she had finished purifying herself (and it assumed for her the likeness of a perfect man).