Numbers 33:8

And so they camped at the Bitter Waters [Marah]. Do not be terrified or afraid when you hear of Bitter Waters. "For the moment all discipline seems bitter rather than pleasant; later it yields the sweetest and most peaceful fruit of righteousness to those who have been trained by it," as the apostle teaches. Then too, the unleavened bread is commanded to be eaten with bitter herbs; nor is it possible to attain the Promised Land unless we pass through bitterness.

Helim [Elim] is where there are twelve springs of water and seventy-two palm trees. You see after bitterness, after the hardships of temptations, what pleasant places receive you! You would not have come to the palm trees unless you had endured the bitterness of temptations. Nor would you have come to the sweetness of the springs unless you had first overcome what was sad and harsh.… And Helim means "rams"; rams are the leaders of flocks. Thus who are the leaders of Christ's flock but the apostles, who are also the twelve springs? But since our Lord and Savior chose not only those twelve but also seventy-two others, there are not only twelve springs but also seventy-two palm trees mentioned in Scripture.

Next they set out from Iroth and pass through the midst of the Red Sea and camp at Bitter Waters. We have said that the time of starting places is a time of dangers. How hard a temptation it is to pass through the midst of the sea, to see the waves rise piled up, to hear the noise and rumbling of the raging waters!

And went three days’ journey in the wilderness of Etham - Called the wilderness of Shur, Exo 15:22. And pitched in Marah - Dr. Shaw supposes this place to be at Sedur, over against the valley of Baideah, on the opposite side of the Red Sea. Stat. 5.