In 1916 Einstein has published the first paper of gravitational wave bu linearize approximation but It contain an error of his calculation then In 1918 he published a new paper of gravitational wave that has a correction of the his last error and conclude that there are the Gravitational wave .He didn't do anything much about gravitational wave but Around 1936, Einstein wrote to his close friend Max Born telling him that, together with Nathan Rosen, he had arrived at the interesting result that gravitational waves did not exist, though they had been assumed a certainty to the first approximation. He finally had found a mistake in his 1936 paper with Rosen and believed that gravitational waves do exist. However, in 1938, Einstein again obtained the result that there could be no gravitational waves!

I don't understand his last work in year 1938 that he conclude that it didn't has the gravitational wave in nature or not?