This surah continues the ideas of the previous surah, which told the story of how, in 570 C.E., around the time of Muhammad's birth, God protected the Meccans (including the ruling tribe, the Quraysh) from an attack by a Christian ruler from Yemen. This army was defeated, this surah claims, to protect the Quraysh tribe and their trade caravans. In response, the Quraysh are encouraged to worship God, Lord of the Ka'aba.
This surah is kind of ironic because elsewhere in the Qur'an, the Quraysh tribe is seen as the opponents of Muhammad's fledgling community of faith. However, further complicating matters is the fact that Muhammad was himself originally a member of the Quraysh tribe. I suppose this surah points out the complex relationship between Muhammad and the Meccan ruling class in the early days of his ministry.