Today, we have Catholic and Orthodox churches (and a few others) using the crucifix, whereas most Protestant denominations use an empty cross in their symbolism. Did this difference in symbolism arise around the time Martin Luther "created" the Protestant church, or did it happen at a different time? Also, what caused the change of symbol?
In history there have always been reasons to show a crucifix without a corpus.1 Especially in the first four centuries of Christianity it was – because of theological reservations – not possible to illustrate the suffering servant figure of Jesus Christ: They thought that it was not beneficial for the majesty of Christ's divinity.2
Another trail leads us to Calvinism: Also there led a sovereign, bordering to the abstract image of God to a sober view of the cross without a corpus.3
1: Burkard Porzelt, Empirische Religionspädagogik, 175
2: Baudler, 1997, 289
3: Baudler, 1997, 57
According to the Catholic Encyclopedia of 1913, whilst the cross was already a symbol of Christianity in the second century (Tertullian says: "We Christians wear out our foreheads with the sign of the cross" [De Cor. mil. iii]), the cross was seen as a punishment and hence a humiliation:
Seeing that the cross was the symbol of an ignominious death, the repugnance of the early Christians to any representation of Christ's torments and ignominy is easily understood.
Yet, crucifixion as a punishment method was latter dropped, not the least because of the Christianisation of the Roman empire:
The punishment of the cross remained in force throughout the Roman Empire until the first half of the fourth century. ... Later on he [Constantine] abolished this infamous punishment, in memory and in honour of the Passion of Jesus Christ (Eusebius, Church History I.8; Schol. Juvenal., XIV, 78; Niceph., VII, 46; Cassiod., "Hist. Trip.", I, 9; Codex Theod., IX, 5, 18). Thereafter, this punishment was very rarely inflicted (Eusebius, Church History IV.35; Pacat., "Paneg.", xliv).
Thus, after a while, it is unsurprising that the crucifixion lost its worst negative connotation, slowly enabling the introduction of crucifixes into private and public spheres:
The crucifix and representations of the Crucifixion became general after the sixth century, on manuscripts, then on private monuments, and finally even on public monuments. ... The earliest manuscript bearing a representation of Christ crucified is in a miniature of a Syriac codex of the Gospels dating from A.D. 586 (Codex Syriacus, 56), written by the scribe Rabula, and which is in the Laurentian Library at Florence. ... Gregory of Tours, in his work "De Gloriâ Martyrum", I, xxv, speaks of a crucifix robed in a colobium, or tunic, which in his day was publicly venerated at Narbonne in the church of St. Genesius, and which he considered a profanation — so far was the public cult of the crucifix from having become general up to that time.
There were still some customary restrictions on representation though (e.g. regarding nudity). Yet, freedom soon emerged:
The last objections and obstacles to the realistic reproduction of the Crucifixion disappeared in the beginning of the eighth century.
As an Eastern rite Catholic, we have our priest holding crucifix to bless us during each divine liturgy. Because Roman rite Catholic, Eastern rite Catholic, Eastern Orthodox, Oriental Orthodox (non-Chalcedonian), and Assyrian Church (non-Ephesian) use crucifix we can safely estimate that this practice date from the early church before schism happened for the first time at 431 in Ephesus.
How and when did Christians start to depict images of Jesus on the cross? Some believe the early church avoided images of Jesus on the cross until the fourth or fifth century. In “The Staurogram: Earliest Depiction of Jesus’ Crucifixion” the March/April 2013 issue of Biblical Archaeology Review, Larry Hurtado highlights an early Christian crucifixion symbol that sets the date back by 150–200 years.
The depiction of Christ on the cross exist along with iconography in the early church. Assyrian Church to this day rarely use iconography due to heavy persecution during the Sassanids. Prior to that Assyrians were known to practice iconography openly. It is highly debated among Christians when iconography was introduced. Some argue iconography at Roman catacombs merely depicting an early corruption of Paganism into Christianity while others argue that it's a direct evidence of an early apostolic practice. Due to its argumentative nature of this debate I try to be neutral and address both viewpoint as neutral as possible. So it's difficult to argue when the empty crucifix symbol occur. Due to the existing crucifix symbol prior to Reformation it can be safely argue that such reform might took place during iconoclastic reformation in the late 16th century Europe.