The correct view is that Hajj was made compulsory in the ninth year AH and Allah did not make it obligatory before that.

Allah has enjoined Hajj upon every adult who is able to do it once in a lifetime; anything more than that is voluntary and an act of worship by means of which one may draw closer to Allah.

Labbayka Allahumma labbayk means: 1- I submit and submit again, 2- I am persisting in obeying You, 3- I confirm my love of Allah, 4- It implies sincerity, 5- It implies drawing close to Allah. 6. It is a symbol of tawhid.