‘But God turned, and gave them up to serve the host of heaven; as it is written in the book of the prophets,
“Did you offer to me slain beasts and sacrifices,
Forty years in the wilderness, O house of Israel?
And did you take up the tabernacle of Moloch?
And the star of the god Rephan?
The figures which you made to worship them?
And I will carry you away beyond Babylon.”
Thus God had turned from them and given them up to serve the host of heaven. Moses himself had warned them against serving the host of heaven (Deuteronomy 4:19; Deuteronomy 17:3) but in Kings it became a regular feature of Israelite worship (2 Kings 17:6; 2 Kings 21:3; etc.). The host of heaven were a poor and blasphemous substitute for the God of Heaven. So once they were in the land God turned away from His people, and handed them over to other gods. (So much for the blessing of the land).
The citation is taken from Amos 5:25-27 LXX. The thought is either that they had professed to worship God for forty years in the wilderness and then had turned, once they were in the land, to the worship of Moloch and Rephan (an Assyrian god). That was how much good the land had done them! Or that the wilderness was not such a time of pure worship as present Judaism tried to make out (it was a constant theme of 1st century AD Judaism that the period in the wilderness had been the time of Israel's purity). For the molten calf demonstrated that it was not a period of pure worship for forty years. Judaism may seek to idealise the forty years in the wilderness, but Stephen is pointing out that it was simply not a true description of that time.
They had turned from the Tabernacle of God to the tabernacle of Moloch. Moloch was the local god of the Ammonites, but was regularly worshipped in Canaan and warned against by Moses (Leviticus 18:21; Leviticus 20:2-5). He was a god who required child sacrifice, and was thus the most to be despised. And the star out of Jacob, God's promised deliverer (Numbers 24:17) had been replaced by the star of Rephan, the god of Assyria. These were the figures that Israel had made in order to worship them. What was more blasphemous than that? Who was it now who had ‘changed the Law of Moses' and exchanged it for idolatry?
We should note here that Stephen is quoting the Bible version that he used (the Greek Septuagint), as we might choose to use a particular version (e.g. ASV RSV TEB NIV) as ‘the word of God'. It was his Bible. What matters is that the general sense is the same.
‘And I will carry you away beyond Babylon.' Stephen changes ‘Damascus' as found in Amos to ‘Babylon' in order to bring home the lesson that they had returned right back to what Abraham had escaped from (Acts 7:2; Acts 7:4). He saw such an alteration as justified because Babylon epitomised all such idolatrous cities (just as when we are preaching we may turn ‘woe to you Chorazin' to ‘woe to you New York'). Israel had turned full circle and had been shown no longer to be God's people.
The Hebrew text of Amos 5:25-27 reads, “Did you bring to me sacrifices and offerings in the wilderness forty years, O house of Israel? Yes, you have borne Sikkuth your king and Chiun your images, the star of your god, which you made to yourselves. Therefore will I cause you to go into captivity beyond Damascus.”
The Hebrew text is not quite as far from LXX as it might seem. ‘Skkth your mlch' is translated by LXX by interpreting the Hebrew as ‘the tabernacle (skkth) of your Moloch (mlch)' vocalising sikkuth as sukkoth (booths). Both recognise that a false god is being spoken of. The name of the god Chiun (an Assyrian god) is simply updated or translated to Rephan (possibly an Egyptian equivalent) in LXX. Again both refer to false gods. The translation problem partly arises from the lack of vowels in the ancient Hebrew text, and probably partly in order to make the names intelligible to the readers of LXX.