What enables the father's mind to change in "Marriage is a Private Affair"?

Part of
Achebe's descriptive strength in the short story is that he does not inundate the reader with
the reasons as to why Okeke changes his mind. He enables the moment within which the change
happens and allows the complexity of this instant of change, what Kushner would call "the
threshold of revelation," wash over the resolution of the story and the reader. It is here
where I think exploration is needed. In terms of the story itself,Okeke receives a letter from
Nene , his rejected and ostracized daughter-in-law, informing him that he has two grandsons who
wish to see their grandfather and that she is sending them along with their father to see him
while she is not. In this, a moment is created in which Okeke realizes that he has moved past
being a father and into the realm of grandfather. He begins to recognize, for a brief instant,
that the disagreement with his son over choice of wife is moot with the present of two
grandsons. Yet, even then, the father wishes to hold on to his resistance, his defiance over his
son's disobedience. However, in a moment, he looks out the window and his resolve to his anger
diminishes:

The sky was overcast with heavy black clouds
and a high wind began to blow, filling the air with dust and dry leaves. It was one of those
rare occasions when even Nature takes a hand in a human fight. Very soon it began to rain, the
first rain in the year. It came down in large sharp drops and was accompanied by the lightning
and thunder which mark a change of season.

In this
connection between the natural world and Okeke's condition, the change of seasons almost
indicates a maturation. It is here in which Okeke realizes that this change also means that
there could be a dark side in that he might never get to see his grandchildren. With only one
son, this is a decision that haunts him, terrifying him and filling him with regret as to both
rejecting them for so long and not getting the chance to do right by them. With the ending of
the story as one in which Okeke "hardly slept- from remorse", it becomes clear that
the combination of this instant, a revelation that goes along with it, and the reflection of its
implications caused by nature all collude to create a condition in which Okeke recognizes his
own folly and seems to be running from his own actions to ensure that such mistakes are not long
term ones.