Very often, the introduction has a different character, meter, and tempo from the main material of the piece (just compare the Introduction (slow) and the main theme (fast) from the Sonata No. 8 "Pathetique" for piano by Beethoven).
Today's piece for sight-reading is Introduction from Introduction, Fugue and Variations on the chorale Christ is erstanden, Op. 15 by Johannes Barend Litzau (1822-1893), a lesser known German Romantic composer.
Here is the score for printing (p. 103). Since this is a Romantic piece, play it legato throughout. If you are curious how the chorale sounds after the Introduction, feel free to sight-read it, too (p. 104-105).
PS Often we play quite literal hymn introductions for church services. However, this piece could inspire you to create your own, musically more interesting Introduction before playing a hymn of your choice.