Rhyme

Not everyone agrees that rhymes are essential to poetry. John Milton famously derided its use in his introduction to Paradise Lost, saying that rhyme is "no necessary adjunct or true ornament of poem or good verse, in longer works especially, but the invention of a barbarous age, to set off wretched matter and lame meter. . ." So Paradise Lost was not rhymed, but metrically excellent.

Rhymes are considered essential in English hymn writing of the metrical kind. I know of only one metrical hymn tune that is regularly set without rhyme: Iste Confessor. Otherwise, rhymes must be employed.

One long-established shortcut, however, is to rhyme only the even-numbered lines. Consider:

Alleluia, sing to Jesus
His the sceptre; His the throne.
Alleluia, His the triumph;
His the victory alone.

There is a solid rhyme on the second and fourth lines. But with the first and third lines there isn't even an attempt at rhyme. The ear accepts this, and simply makes the rhyming lines longer, ignoring the break after "Jesus" and "triumph." However, the break is real. This hymn, for example, is often set to Hyfrydol, which is considered an 8787 Double hymn--with alternating lines of eight and seven syllables, not of 15 syllables. But the ear makes accommodations.

Rhyme is an aid to memory. Commercial jingles that rhyme are easier to remember; if you can remember the first line, it acts as a prompt for remembering the next. In my hometown there used to be a jingle (probably still in use) that went,

"See Pearson Ford, they stand alone
At Fairmount and El Cajon."

Rhyme is one of the reasons that hymns are more often remembered on Sunday afternoons than sermons are.