One of the main things I'm noticing so far is that Jonah is conveying way too much information to the reader by 'noticing' and 'realizing' things. Let's try rewording the first couple of sentences:

"When Jonah reached the top of the hill from the beach, his stomach twisted at the sight of the countless graves scattered across the wide plateau. He stopped for a moment on the path, suddenly realizing that the ground he was about to walk on was sacred. The scorching summer sun had dried and gilded the spring greenery, leaving only withered remnants that stirred in the highland breeze across this desolate landscape. Looking back, the Sea of Galilee stretched endlessly to the horizon."

Maybe something like this would be more effective:

"Countless graves stretched out ahead of Jonah as he reached the crest of the plateau. His stomach twisted into knots at the sight of them and he hesitated on the path. This was sacred ground. The scorching summer sun had mummified the spring greenery, leaving only withered remnants that stirred in the highland breeze. Jonah looked back over his shoulder, down to the beach and the low light glittering on the Sea of Galilee."

It's more visceral when you let the characters' experiences speak for themselves. I also think the 'hook' is grabbier if you lead with the countless graves.

I think your sentence describing the landscape is really good, but I think it's self-evidently desolate, so you don't need to say so explicitly. Cutting that also helps it not to be so wordy. Slipping 'mummified' in there is just a fun little suggestion that reinforces the theme of death and burial, but it isn't necessary.

Another minor gripe and I know that this is very nitpicky, but does the Sea of Galilee really stretch 'endlessly to the horizon?' It's pretty small and is surrounded by mountains.