The Quran

يَعمَلونَ لَهُ ما يَشاءُ مِن مَحاريبَ وَتَماثيلَ وَجِفانٍ كَالجَوابِ وَقُدورٍ راسِياتٍ ۚ اعمَلوا آلَ داوودَ شُكرًا ۚ وَقَليلٌ مِن عِبادِيَ الشَّكورُ

Muhammad Asad

they made for him whatever he wished of sanctuaries, and statues, and basins as [large as] great watering-troughs, and cauldrons firmly anchored.¹ [And We said:] "Labour, O David's people, in gratitude [towards Me]² - and [remember that] few are the truly grateful [even] among My servants!"³

I.e., because of their enormous size. Cf. II Chronicles iii, 10-13, where statues ("images") of cherubim are mentioned, as well as iv, 2-5, describing "a molten sea" (i.e., basin) of huge dimensions, resting upon twelve statues of oxen, and meant to contain water "for the priests to wash in" (ibid., iv, 6). Tbe "sanctuaries" were apparently the various halls of the new temple.
These words, ostensibly addressed to "the people" or "the family" of David, are in reality an admonition to all believers, at all times, since all of them are, spiritually, "David's people".
I.e., even among those who consider themselves God's servants - for "truly grateful [to God] is only he who realizes his inability to render adequate thanks to Him" (Zamakhshari).