What does it mean to be 'gathered to the name of the Lord Jesus alone'?

I received a letter from someone in the UK which, twice, used this expression and I wonder what it was meant to convey, especially the word 'alone'. Is this a saying of a particular group of self-identifying Christians ? If so, what are they communicating by the 'alone' ? Are they implying that no other matters can be included as a ground of gathering ? And why is the title 'Christ' not mentioned, or 'Son of God' ?