She said, "My Lord, how will I have a child when no man has touched me?" [The angel] said, "Such is Allāh; He creates what He wills. When He decrees a matter, He only says to it, 'Be,' and it is.
((Remember) when the angels said: "O Maryam! Verily, Allah gives you the glad tidings of a Word from Him,) a son who will come into existence with a word from Allah, `Be', and he was. This is the meaning of Allah's statement (about Yahya)
مُصَدِّقاً بِكَلِمَةٍ مِّنَ اللَّهِ
(Believing in the Word from Allah.) 3:39, according to the majority of the scholars.
The glad tidings given by the angel (verse 46) regarding the birth of Sayyidna ` Isa without a father surprised Sayyidah Maryam as she was a virgin. She wondered how it would happen. Would that be a Divine miracle or would she be asked to marry a man? The Divine answer eliminates the latter possibility. Not restricted by it, 'Allah creates what He wills', that is, His will is all sufficient to bring some-thing into existence. He needs no medium or cause. It is only His command "be" which makes things come into existence.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 44–47
God blessed Zachariah (Zakariyya) with an offspring in his old age; provided sustenance to Mary in her shrine; created Jesus without a father, and brought into being chaste and upright people who were descendants of Abraham, so that they could be chosen to communicate the message of God to human beings. God did not grant these blessings to His people for no good reason: He found them so deserving that he showered them with His blessings. These were the people who had no material expectations from their children; their happiness rested upon their children’s dedication and devotion to the cause of God. These were the people who wanted their children to be safe from Satan and join the band of believers. They were not given to jealousy and ill-will on seeing goodness in others. It was through their good influence that their children too were in control of their selves and became one with those who truly remembered God: who chose the right way, abandoning the path that leads one astray. Such are the people whom God provides for out of His special mercy, and who have His special blessings showered upon them.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.