What is Modernism? How do we reject it?

[Wretched_1]

Pope Pius X was greatly concerned to prevent the infiltration of Modernism which is the Mother of all Heresies? How do we prevent Modernism which was likely the smoke of Satan of which he spoke infiltrating the Church & her theology?

 

[Genesis315]

Modernism is a heresy that says there is no objective revelation from God to the human race, on which Christianity is finally based, nor any reasonable grounds for credibility in the Christian faith, based on miracles or the testimony of history. Faith is, instead, just an internal impulse and so doctrine can change as individual and collective consciousness changes.

Because it denies revelation itself, it denies all dogmas, and is therefore the “synthesis of all heresies.”

We reject it by adhering with divine faith to the entire deposit of faith as revealed by God and handed on by the Church.

 

[Wretched_1]

So was it wrong for St Pius X to be concerned with Modernism? Should he not have been concerned that novelties being introduced to the Liturgy novelties in Theology, might confuse the faithful and put their immortal souls in jeapordy?