Sidi and Baroka embody traditional notions of womanhood and manhood respectively. Sidi is a beautiful woman, and her beauty is a source of near-universal admiration. In the traditional village society in which she lives, great store is placed upon a woman's beauty, not least because it greatly enhances her prospects of finding a suitable husband. And Sidi has every intention of finding such a man, a sure indication that she's determined to remain true to Yoruba tradition.
As indeed is Baroka. He's very much the living embodiment of the tribal Alpha male. He is lord and master in his own home, and sees women as existing purely to cater to his own whims. Not surprisingly, given Sidi's extraordinary beauty, Baroka thinks that she would make a worthwhile addition to his already enormous family. As both Sidi and Baroka are committed to the maintenance of tribal tradition, it would seem that theirs is a match made in heaven.
Yet there is a big difference between their respective attitudes. Baroka's motives for paying homage to ancient custom and tradition are largely self-serving. It's men like him who derive the most benefit from current social arrangements. At the same time, he's also smart enough to realize that the world outside is changing and will continue to change. We see this point illustrated in his desire to have Sidi's beautiful image printed on stamps. This shows us that Baroka, for all his adherence to tradition, retains a connection to the modern world.
As for Sidi, she's too young, innocent, and shallow to understand that Baroka's exploiting her. Like many young women in her position she looks at prevailing customs as providing her with a sense of security, giving her and any future children she may have an assured place in tribal society.