神 (kami) is god and God in one word, the kami of a shrine and the Christian deity alike; は (wa) marks the subject; 偉大 (idai) is great by excellence, outstanding, and where the same characters can mean huge in Chinese, in Japanese they cannot. The four characters are written as a title is written, with the closing word of the sentence left off, and a Japanese reader completes it without thinking.
It is a correct translation of the English sentence, and the completed sentence has a fixed home in Japanese that a buyer should know: 神は偉大なり, God is great, is the Japanese for the Islamic takbīr, Allāhu akbar, in the encyclopedias and the histories, while the Japanese Bible says the LORD is great with a plainer word, 大 (dai), and always has.
The English has the same double life, Great is the LORD and the takbīr's usual rendering in one phrase, and the design carries it honestly: a Christian reader hears the Psalm, a Japanese reader may hear the other confession first, and the words are true in both. God is Great in Japanese is 神は偉大 which is read kami wa idai. 神 (kami) is god, and 偉大 (idai) means great in the sense of mighty or magnificent, not large.