The Republican Party has been a fusion of business elite and evangelical Christians since its inception. The two groups not only broadly overlapped, see https://en.wikipedia.org/wiki/Quakers, but both had adverse interests to the slaveholding south. The religious segment opposed slavery, and the business segment favored economic policies favorable to manufacturing industry (e.g. a strong currency, tariffs, and infrastructure) versus the weak currency and low tariffs favored by the agricultural south.

The strength of each faction waxes and wanes depending on what’s dividing the electorate. During the mid-20th century, both parties embraced “Christian values” (https://content.gallup.com/origin/gallupinc/GallupSpaces/Pro...) so economic issues dominated. Since Clinton, the parties are generally both on board with neo-liberalism, so religious and social issues dominate.