2. With reference to verse 41, Sayyidna Zakariyya's purpose behind requesting a sign (of pregnancy) was to be happy at the prospect and thus be enabled to show their gratitude all along even prior to the ac¬tual birth of the child. So, Allah gave him the sign stated above.
The sign given was remarkably suitable to its purpose. His request for a sign was prompted by his wish to show his gratefulness. Now, the sign set for him leaves him incapable of doing anything but this. Even a hundred signs would have not done what this one sign did and, of course, the noble purpose he had on his mind was all too well-accomplished. (Bayn al-Qur'an)
The last phrase: (except through gestures) in this verse tells us that in a situation where speech is not possible because of a valid reason, gesture would be deemed as its substitute. Consequently, it appears in a hadith that the Holy Prophet (صلی اللہ علیہ وآلہ وسلم) asked a maid-servant: این اللہ ؟ I ('Where is Allah?' ). She pointed out towards the sky. He said: 'This maid-servant is a Muslim.' (al-Qurtubi)