Which had made this conspiracy - This oath συνωμοσίαν sunōmosian, this agreement, or compact. This large number of desperate men, bound by so solemn an oath, would be likely to be successful, and the life of Paul was therefore in special danger. The manner in which they purposed to accomplish their design is stated in Acts 23:15.

And they were more than forty which had made this conspiracy. Who met together, formed this resolution, entered into this scheme, and bound themselves with this oath; the word rendered "conspiracy", signifies an agreement by oath; such a number of them banded together, that they might have strength sufficient to take Paul out of the hands of the soldiers, as he was conducted by them from the castle to the temple.

Conspiracy (συνωμοσίαν)

Lit., swearing together; conjuration. According to its etymology, conspiracy is a breathing or blowing together (Latin, conspirare). Hence, of concerted thought and action.

And they were more than forty which had made this conspiracy.

23:12-15 Certain of the Jews banded together. Perhaps these Jews were of the bitter enemies from Asia who had laid hands on him in the temple. They may have belonged to a wild fanatical association of Jewish assassins, who, a few years later, played a prominent part, called Sicarii. The Talmud says that those who took such a vow were released from it, if it was impossible to carry it out. Their purpose was to induce the chief priests, who were Sadducees, to have Paul appear before the Sanhedrin the next day, and then they would murder him.

23:12-24 False religious principles, adopted by carnal men, urge on to such wickedness, as human nature would hardly be supposed capable of. Yet the Lord readily disappoints the best concerted schemes of iniquity. Paul knew that the Divine providence acts by reasonable and prudent means; and that, if he neglected to use the means in his power, he could not expect God's providence to work on his behalf. He who will not help himself according to his means and power, has neither reason nor revelation to assure him that he shall receive help from God. Believing in the Lord, we and ours shall be kept from every evil work, and kept to his kingdom. Heavenly Father, give us by thy Holy Spirit, for Christ's sake, this precious faith.