The Quran

اللَّهُ نَزَّلَ أَحسَنَ الحَديثِ كِتابًا مُتَشابِهًا مَثانِيَ تَقشَعِرُّ مِنهُ جُلودُ الَّذينَ يَخشَونَ رَبَّهُم ثُمَّ تَلينُ جُلودُهُم وَقُلوبُهُم إِلىٰ ذِكرِ اللَّهِ ۚ ذٰلِكَ هُدَى اللَّهِ يَهدي بِهِ مَن يَشاءُ ۚ وَمَن يُضلِلِ اللَّهُ فَما لَهُ مِن هادٍ

Muhammad Asad

God bestows from on high¹ the best of all teachings in the shape of a divine writ fully consistent within itself, repeating each statement [of the truth] in manifold forms² - [a divine writ] whereat shiver the skins of all who of their Sustainer stand in awe: [but] in the end their skins and their hearts do soften at the remembrance of [the grace of] God.... Such is God's guidance: He guides therewith him that wills [to be guided]³ - whereas he whom God lets go astray can never find any guide.⁴

Lit., "has been bestowing from on high", i.e., step by step. The verbal form nazzala indicates both gradualness and continuity in the process of divine revelation and may, therefore, be appropriately rendered by the use of the present tense.
This is the most acceptable meaning, in this context, of the term mathani (p1. of mathna), as explained by Zamakhshari in his commentary on the above verse. Another possible meaning, preferred by Razi, is "pairing its statements", i.e., referring to the polarity stressed in all Qur'anic teachings (e.g., command and prohibition, duties and rights, reward and punishment, paradise and hell, light and darkness, the general and the specific, and so forth). As regards the inner consistency of the Qur'an, see also 4:82 and 25:32, as well as the corresponding notes.
Or: "He guides therewith whomever He wills", either of these two formulations being syntactically correct.
See note 4 on 14:4.