TAKEN OR NOT... ONLY A REMNANT OF THE SAVED WILL BE RAPTURED?... IS THIS GRACE OR WORKS OR ANOTHER GOSPEL?

Is this Grace or Works or another Gospel?... and what about sanctification?

Rom 3:10
As it is written:
“There is none righteous, no, not one;

2Co 11:3-4
But I fear, lest somehow, as the serpent deceived Eve by his craftiness, so your minds may be corrupted from the simplicity that is in Christ. For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it!

Please watch until end for context...

Rom 9:27
Isaiah also cries out concerning Israel:
“Though the number of the children of Israel be as the sand of the sea,
The remnant will be saved.

Mat 24:40
“Then two men will be in the field: one will be taken and the other left.

Were both men Christians?