What does قِرَاءَةً وَاحِدَةً express in قَرَأْتُ الرِّسَالَةَ قِرَاءَةً وَاحِدَةً?

Maf'ul Mutlaq: Emphasis, Quality and Number

• the reader
• one occurrence of reading
• the letter that was read
• the place of reading