Church marriages in the Middle Ages were only for aristocrats and royalty, and the main incentive was that a priest (or better, a bishop) was a credible witness for the vows. Ordinary people made their vows in front of their community.
Around 1520, Martin Luther confirmed that marriage was a “worldly thing”: no business of the Church, but in 1563 the counter-reformation Council of Trent declared that a Roman Catholic marriage must have a priest. Protestants throughout Europe continued to have civil marriages, but in 1753 the Marriage Act made a church ceremony mandatory in Great Britain. (for Anglicans. Some other Christian sects and other religions were allowed to carry on with their own practices.) That was how it stayed until 1836, when a new Marriage Act provided for civil ceremonies in all cases. At this date, the Act applied to Ireland.
So the idea of the Church being involved in marriages was at one time “a new thing”, something that the clergy had just invented.
But somehow, the new nation of Ireland incorporated a Church-defined definition of marriage into its constitution. (I say “somehow”, but we all know exactly how it was. Tentacles of doom, infiltrating every sphere of life.)
The people of Ireland voted today to change the constitution. Actually, it’s arguable that marriage isn’t even a constitutional issue (it isn’t in the UK; just regulated by Acts of Parliament) but no matter, the situation is better than it was before, and two-thirds of the voters made it so.