In The Crucible, how does the scene where John Proctor tries to recite the commandments move the plot forward?

This is of course is a moment of high drama in Act II. As
Hale questions John and Elizabeth, he makes it clear the way that any sign of weakness
or omission of holiness can be regarded as a potential sign of witchcraft. Note what he
says with unerring accuracy:

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Theology, sir, is a fortress; no crack in a
fortress may be accounted
small.

What he is blind to is
the way that John Proctor's omission of the sin of adultery is actually a perfect
example of dramatic irony. We and Elizabeth and John both know that John has had an
adulterous relationship with Abigail, and his inability to recite this commandment
reflects his inability to own up and be honest about his own sin. Of course, this scene
also foreshadows the time when John confesses his adultery openly in one last ditch
attempt to prove that Abigail and the other girls are making up their stories. Thus this
scene plays a very important part in terms of how it advances the plot of the play
through its use of dramatic irony and how it foreshadows what is to come in Act
III.