But in relation to the spectators of the miracle--and it is they who are in question here--miracle is the causa efficiens of faith.
In relation to the miracle-worker faith (confidence in God's aid) is certainly the causa efficiens of the miracle.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "efficiens" in a variety of sentences. We hope that you will now be able to make sentences using this word.