Einstein did not plagerize Hilbert. He used Hilberts math as the most accurate representation of his own theories of relativaty. Until then, no one realized that space was curved by gravity. All physicists find a mathematical model for their theories often from pure mathematics which had no relationship to the physical theory when originally developed. That's why it is refered, to as "pure mathematics". The applications usually come later through physics. I'm sure you must be reading too much of your science from the old Soviet Union texts and are convinced that the Russians invented the automobile, airplane, and toilet paper.

Einstein received a copy of Hilbert's work on 18 November 1915. Hilbert delivered his lecture to the Goettingen Academy on 20 November 1915. Einstein betrayed Hilbert's trust and plagiarized Hilbert's work on 25 November 1915. Five days before Einstein submitted his 25 November paper Hilbert had submitted a paper The foundations of physics which also contained the correct field equations for gravitation. Hilbert's paper contains some important contributions to relativity not found in Einstein's work.