1 Tim 2:5 is a verse that many Protestants will use to try to discredit the Catholic Church's practice of praying to Mary and the saints for intercession. However, if one looks at the Greek that Paul used their argument is dispelled immediately.
For example, for the word "One," Paul uses the greek word heis which means "one", "first", or "primary."
Paul could have used the greek word monos meaning "sole", "only", or exclusive one" if he wanted to refer to the mediation of Christ as completely exclusive.
But he didn't.
Christ is the Perfect mediator from whom all secondary mediation is made possible.
As Lumen Gentium 62 teaches:
"No creature could ever be counted along with the Incarnate Word and Redeemer; but just as the priesthood of Christ is shared in various ways both by his ministers and the faithful, and as the one goodness of God is radiated in different ways among his creatures, so also the unique mediation of the Redeemer does not exclude but rather gives rise to a manifold cooperation which is but a sharing in this one source."