The announcement of George's visit in Act I creates a level of tension for Ann, Chris, Kate and especially Joe Keller. It serves to open the past events and bring the incident with the faulty airplane parts into the present moment. George's actual visit is a very significant turning point in the play.
George's visit is the catalyst that ignites the tragic ending of the play. For Ann, George's visit brings both heartache and hope. Heartache, because once the truth is told about Joe Keller's framing of Steve, Ann could never marry Chris. Hope because now she can embrace her father once more, she has not spoken to him or seen him for a long time.
George's visit serves to initiate the unveiling of the truth for both Kate and Chris, and leads to the overwhelming sense of guilt that Joe Keller feels which results in his committing suicide.
Kate must face the truth about her son Larry's death, something that she has refused to do until the end of the play.
Chris, who has been idealistic throughout the play, comes face to face with his father's immorality and guilt over the death of the pilots and the suicide of his brother Larry.
The news of George's visit, coming at the end of Act I, brings a mixed reaction from the main characters. Chris and Ann don't seem particularly worried about the news. Chris, especially, does not feel that George will be bringing trouble, but this is because Chris is the one who is most in the dark about the truth. Ann, knowing what she knows about the truth of Larry's death, may have a glimmer of an idea that George may be a less than positive visitor, but being in love and with Chris may cloud her thinking about this. Joe and Kate, however, are very nervous about what George may be coming for. They are aware of the truth (Joe is consciously aware, Kate is in denial), and are worried what trouble he will be stirring up.
The news brings the act to an end on an uneasy note. The audience is well aware that George's arrival will likely add tension to the proceedings.