What purpose do steeples serve? Are they put high up on church buildings as some sort of marketing tool so it can be seen from far away or is there some other reason(s)?
Interesting question. I managed to find an article, The History of Church Steeples, that actually addresses this.
One reason: It was simply an architectural style that happens to inspire us to look heavenward.
These early church architects designed grand cathedrals and churches that had intricate, soaring steeples. The vertical lines of the steeple helped to visually enhance the lines of the church, directing the viewers' eyes vertically to the heavens. Obviously, this verticality complements part of the mission of the church, to keep us in a heavenly frame of mind, but from an architectural standpoint, this vertical lift gives the architecture a more graceful and pleasing look. The shorter the building, the more squat the appearance; the taller the building, the more graceful it becomes. The early church believed that the church could communicate the truth of the Bible in pictures and symbols to those who were illiterate, such as using the picture in the stained glass to tell stories, as well as the steeple, which helped by pointing upwards devotedly to Heaven. Therefore, the steeple has a dual role in that it helps the congregant in his or her spiritual mindset, and the steeple also helps the architect with a design feature that enhances the overall harmony of the architecture.
In short, there's no doctrinal significance, or symbolic other than the pointing to the Heavens. It's simply a beautiful style that, once done, was imitated throughout the ages until it became expected.
Because steeples have bells in them
See, they know they need to pray the Angelus because the bell is ringing.
for the sound of bells to carry over the tops of buildings, the bells had to be higher than surrounding buildings. Bells were used not only before church service, but also to notify people of emergencies, such as fires. The buildings were regularly used as a town meeting place, as well, not like today where they are often locked except on Sunday mornings.
The church has always been recognised as a patron of art as it has needed to use art for teaching and inspiring . Stained glass windows often contained depiction of scriptural teachings, and allegorical interpretation lent itself particularly well to this form. Common folk found pictorial depiction easier to understand.
Thus the Samaritan would be depicted as Christ, the wounded man as man under sin's oppression.
The other way art could be used was for inspiration . Cathedrals have been called prayers in stone, depicting the heavenward soaring of men's words.
People entering a place of worship were inspired to believe they were seeing and hearing men praising God through architecture and music. God was the recipient of this worship, and men's energies were used to create forms in a way that reflected this. Conscious effort was made in the soaring interiors and ethereal singing to convey the idea that God was present in all His Majesty.
Compare this with contemporary architecture and music, where the end products have the consumer in view. Churches are patronised because they have comfortable seating, climate control and theatre acoustics, the better to hear words that comfort and beats that stir the feet to tap.