The Left originates in the French Revolution, and is associated with ideas that find their origin in the Left of the French Revolution. Burke did an an able early critique of the French Revolution and its Leftist proponents: https://polsci.institute/western-political-thought/edmund-burke-criticism-french-revolution/ . He objected to its attempt to divorce the Christian religion from politics, and its advocacy of secular humanism as its replacement. Here is a later but similar critique from a Christian perspective: https://www.sermonaudio.com/sermons/21081143182 .
Principal pillars of the Left in our own day include:
1. Mass migration (to convert the USA as a homeland for Christian Americans into a modern globalist Babel with one world socialist government rooted in secular humanism)
2. Democratic socialism or Marxism
3. Net Zero agenda
4. LGBTQ agenda
5. No or low tariffs
6. Pro-EU and pro-WEF, which have promoted the globalist world order based upon secular humanist tenets
7. Domestic alliance of convenience with Islam
8. Pro-UN and Pro-UN Agenda 2030, which have promoted the globalist world order based upon secular humanist tenets
9. Legalized abortion
10. Against Second Amendment gun rights
11. Condemnation of Christian American history and influence in North America, such that reparations are owed today to various and sundry groups. It views European colonization and settlement of the Americas as a net evil rather than the net good it has been by virtue of Christianizing influence.
Western Leftism is the principal opponent of historic Christian nations and has been an important instrument in keeping the West wedded to secular humanism. It is especially antithetical to historic Christian America.
A counter-balancing truth is that the Left does not have a monopoly on sin, and those on the conservative Christian right should not dismiss every criticism of the Left without proper consideration, for God has given to all mankind a conscience. Even those deep in sin and rebellion themselves on the Left are capable of identifying real sins in Christians. God can use and has used those on the Left to hold those on the conservative Christian right accountable for various of our sins. All of fallen humanity, including Christians, are sinners in need of constant examination.