Praise be to Allaah.
The answer is in two parts:
In general terms, every believer must believe that every action of Allaah has great wisdom behind it, and there is no need for it to be explained in full to every person. This is a kind of test, as Allaah says (interpretation of the meaning): “… that He may test you which of you is best in deed…” [al-Mulk 67:2]
To answer this question in more detail: the Qur’aan was revealed in the language of the Arabs, and in Arabic it is as correct to use the plural when speaking of one person as it is to use the singular. But the plural is used for respect and glorification, and no one is more deserving of respect and glorification than Allaah. So the singular is used to affirm the fact that He is One and has no partner or associate, and the plural is used to affirm His glory and majesty, may He be exalted.
Ibn Taymiyah (may Allaah have mercy on him) wrote in Majmaoo’ al-Fataawaa (5/128) some words which may be of interest to us here:
“With regard to Allaah’s closeness to us, sometimes it is mentioned in the singular, as in the aayah (interpretation of the meaning): ‘And when My slaves ask you (O Muhammad) concerning Me, then (answer them) I am indeed near (to them by My knowledge). I respond to the invocations of the supplicant when he calls on Me…’ [al-Baqarah 2:186] and the hadeeth: ‘The One on Whom you call is closer to any one of you than the neck of his riding-camel’, and sometimes in the plural, as in the aayah (interpretation of the meaning): ‘… And We are nearer to Him than his jugular vein’ [Qaaf 50:16]. This is like the aayaat (interpretation of the meanings): ‘We recite to you…’ [al-Qasas 28:3] and ‘We relate unto you…’ [Yoosuf 12:3]. Such usage in Arabic refers to the one who is great and has helpers who obey him; when his helpers do something by his command, he says ‘We did it,’ as a king might say, ‘We conquered this land and we defeated this army,’ and so on.”
Further important details may be found under question # 606 . And Allaah knows best.