But it is not eternal. Not forever. By God’s design.
1 Cor 3:
11 For no other foundation can any one lay than that which is laid, which is Jesus Christ. 12 Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, stubble— 13 each man’s work will become manifest; for the Day[b] will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. 14 If the work which any man has built on the foundation survives, he will receive a reward. 15 If any man’s work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.
That process is after one dies, but it’s temporary, NOT eternal. The person who goes through this, died without mortal sin. After this purification, they go to heaven.