The so-called lazy ways of Unoka are a negative symbol for his son Okonkwo. Because his father poor, and dies owing many debts, he is said to have lived his life by following feminine energy. This is an embarrassment to Okonkwo, who decides to be just the opposite of his father, in masculine energy and who garnishes many titles and riches.
Achebe uses this contrast to show that although the Igbo's have a rich cultural life, there are dangerous divisions that will later lead to the downfall of that culture. Although Okonkwo seems to be the ideal Igbo male, he is really living his life in fear of being like his father. That is why his son, Nwoye, is such a disappointment to him. Nwoye seems more like his mother than his father and this feeds his father's fears that his owon so may be like his father.
When Ikemefuna comes, Okonkwo takes an immediate liking to this masculine boy and hopes this boy's personality will rub off on Nwoye. Unfortunately, Ikefefuna's execution is ordered and it is Okonkwo, fearing he will be thought a coward, who commits the execution. This has a lasting effect on Nwoye, who rejects the ways of his father and is left open to the message of the white missionaries who appear just as Okonkwo is banished to his mother's land.
While Okonkwo is gone, Nwoye becomes a part of the missionary church, something that embarrasses Okonkwo even more. When Okonkwo returns, he cannot accept the changes the missionaries and the white government have brought to the Igbo people. He ends up committing suicide. In the end, the Igbo people have been changed from a strong band of villages to a subservient people to the white colonists because their society and beliefs lead to weaknesses within their own tribe.