Title of Our Lord, referring to His reconciliation of God and man.
The Council of Trent defines that "we were saved through the merits of one mediator Our Lord Jesus Christ".
The object of the mediatorship is here pointed out as the salvation of mankind, as Saint Paul wrote (1 Timothy 2; cf. Colossians 1).
Christ is well qualified to be a mediator, i.e., one who brings estranged parties to amicable agreement.
Being God and man, He can best restore friendship between God and the human family, and bring peace to men, His brethren, who through Him have become the objects of God's complacency, as the angels sang in midnight heavens: "Peace to men of good will."
Even if man had not sinned and the Incarnation had not taken place, Christ would be our Mediator, to offer to God mankind's homage thus deified, "Glory to God in the highest," and bring God's blessings down upon men.
He is the head of the body, the Church, the firstborn of every creature, our human family thus acquiring a claim to participate in the supernatural privileges of our head, Christ Jesus the Son of God.
As Wilhelm well says, "His mediation partly replaces, partly completes, partly renders possible and efficacious the saving work of man himself," for personal salvation and sanctification are effected by our own free acts as members of Christ, enabled by the Communication of life Divine to do godly acts and really merit our eternal reward when Christ our Mediator will achieve His triumph.
New Catholic Dictionary