Different editions of Shakespeare’s plays often offer different accountings of the plays’ line numberings (especially if prose passages are involved).  Therefore, when asking about a specific passage, it’s helpful to give the first and last lines of the passage in which you’re interested.  Lines 198-205 in the Open Source Shakespeare, for instance, include the following lines:

Hermia. God speed fair Helena! whither away?

Helena. Call you me fair? that fair again unsay.

Demetrius loves your fair: O happy fair! 190

Your eyes are lode-stars; and your tongue's sweet air

More tuneable than lark to shepherd's ear,

When wheat is green, when hawthorn buds appear.

Sickness is catching: O, were favour so,

Yours would I catch, fair Hermia, ere I go; 195

My ear should catch your voice, my eye your eye,

My tongue should catch your tongue's sweet melody.

Were the world mine, Demetrius being bated,

The rest I'd give to be to you translated.

O, teach me how you look, and with what art 200

You sway the motion of Demetrius' heart.

Hermia. I frown upon him, yet he loves me still.

Helena. O that your frowns would teach my smiles such skill!

Hermia. I give him curses, yet he gives me love.

Helena. O that my prayers could such affection move! 205

Hermia. The more I hate, the more he follows me.

Helena. The more I love, the more he hateth me.

Hermia. His folly, Helena, is no fault of mine.

Helena. None, but your beauty: would that fault were mine!

This passage employs a number of literary devices. Rhyme, for instance, is used throughout the passage, as are couplets.  The use of rhymed couplets enhances our sense here of a two-part dialogue. Repetition of the word “fair” is used in lines 188-90, while repetition of the word “catch” in lines 194-97. Metaphors appear, for instance, in lines 191-92, especially in the description of eyes as “lode-stars.” Rhetorical balance appears within line 193, within lines 196-97, and within lines 202-09. Alliteration appears in the first three words of line 198 and in the second and sixth words of line 208 (as well as elsewhere).  Most significantly, a method known as stichomythia appears in lines 202-09. Dictionary.com defines stichomythia as

dramatic dialogue, as in a Greek play, characterized by brief exchanges between two characters, each of whom usually speaks in one line of verse during a scene of intense emotion or strong argumentation.

The effect of stichomythia in this exchange is to emphasize the strong contrasts between the situations of Hermia and Helena. Another effect is to make the language sound somewhat contrived and artificial and thus far more suitable to a comedy than to a tragedy. This is especially the case in the present passage since a strong sense of balance exists not only between the lines but within them. People rarely speak this way in "real" life, and so the artificiality and silliness of the speech is emphasized here. It is hard to take such speech seriously, and that is why such speech is perfectly appropriate to a comedy.