Joshua 3:4 - Matthew Poole's English Annotations on the Holy Bible

Two thousand cubits make a thousand yards, and at which distance from it the Israelites seem to have been encamped in the wilderness. And because they generally went from their tents to the ark to worship God, especially on the sabbath days, hence it hath been conceived that a sabbath day's journey reached only to two thousand cubits. But that may be doubted; for those who encamped nearest the ark were at that distance from it, and came so far; but the most were farther from it, and their sabbath day's journey was considerably longer. Come not near unto it; partly from the reverent respect they should bear to the ark; and partly for the following reason. That ye may know the way by which ye must go; that the ark marching so far before you into the river, and standing still there till you pass over, may give you the greater assurance of your safe passage.