Mysteries

It's hard to find a good explantion of this. It's usually just "you know, the mysteries".

But this seems to be a good working definition from Wikipedia:

"those holy acts through which the Holy Spirit mysteriously and invisibly confers Grace (the saving power of God) upon man."

Examples include Baptism, Confirmation, Repentance, the Sacrament, Marriage, Ordination, Endowment, Sealing

Divine acts through which I receive an increased capacity to utilize His power, as opposed to a temporary infusion of power, such as when the Spirit guides me through a particular trial.

Mysteries are the ordinances through which I am permanently strengthened. Which strengthening is difficult, if not impossible, to explain in secular terms.

I think the mystery is the explanation of how the ordinance confers power.