‘And a mouth speaking great things and blasphemies was given to him and he was given authority to continue for forty two months.'
This refers to the head that was smitten to death and was healed (v. 3). ‘Was given to him'. Up to now this phrase has signified God's permitting. Now it has a twofold meaning. Outwardly it is the Serpent who ‘gives' his authority to him, but John recognises that behind this, as behind all things, is God (compare 1 Chronicles 21:1 with 2 Samuel 24:1).
The claim to Imperial divinity was first emphasised under Augustus (although earlier Caesars were accepted as divine by many), but it was Gaius Caligula who assiduously propagated such a belief in his own divinity throughout the Empire, and even sought to enforce it by force among the Roman aristocracy who naturally were most wary of his claims. While the Roman aristocracy were happy to see the common people worshipping the Emperor, they were the last to believe in the divinity of Emperors, for they knew them too well, and under Caligula some of them suffered for it.
He also included in his efforts the aim of setting up his image in the Jerusalem Temple, and images in other places, and he reacted against any attempts to deny him worship. Tiberius had laid little emphasis on the Imperial cult. Caligula brought it to the fore. This would naturally result in many conflicts with Christians who at various times would find themselves in a position where they had to deny his deity and refuse to offer sacrifices to ‘Rome and the Emperor'. (Historically he is not viewed as strictly a wholesale persecutor of Christians per se, for he persecuted everybody, but contemporary Christians who suffered and saw others suffering under his claims no doubt saw it differently).
His reign was the first in which emperor worship became a major issue and lasted for three years and ten months. John sees this is significant and dates from the early part of his reign, putting it in terms of prophetic terminology as ‘forty two months' (between three and four years - note that the forty two months is not strictly said to be the length of his reign, thus a short period can be seen as excluded at the beginning before his persecutions really got under way).
As we have mentioned Tiberius had not been an enthusiastic propagator of his divinity, and the shock with which Caligula's emphatic proclamation of divinity and demand for worship from all was received by Christians is clear from John's reference to it here. It brought a new perspective to, and emphasis on, Emperor worship which boded ill for the future. But in the end it is not the specific activity of Caligula that is finally in mind but the continued activity of the wild beast.