A practical reason could be that, as they were about to enter the Promised Land, the pillar of cloud was no longer going to lead them by day. It was the Lord their God “going before them in a pillar of cloud by day, to lead them in the way, and by night in a pillar of fire, to give light to them, to go by day and by night” (Exodus 13:21 YLT). A footnote on Exodus 40:36:36 in The Companion Bible states:
“This continued till Moses’ death, when the ark (which till then was
carried in the midst of the host) took its place and “went before
You ask for a practical reason for the statement, “... ye have not passed this way heretofore” and I think it is that they needed to follow an exact route to get to the exact place by Jordan’s bank where the priests were to walk into the water, only after which would God display his miraculous power in then parting the waters. As they had not been that way before and did not know where, exactly, God wanted them to make entry into the river, he alone could lead them, and the ark was the visible guide to ensure that those millions of people and their animals would not try crossing the river at the wrong place. In unfamiliar territory, even a slight degree of divergence from the route can lead to serious trouble, as I found out when I persuaded my husband to follow me to return to a holiday home at dusk. We had never been that way before, only knowing that a mountain was behind our abode, with lochs on either side of the mountain. I thought the wedge shape of the mountain required us to go a certain way to keep to the correct side of it, but walking just a degree out, we ended up on the wrong side of the mountain and had to back-track many miles in darkness.
The ark would lead the way, going before (ahead of) them. The great distance between it and the following multitude might signify two things. First, that the ark did not need to be surrounded by the people, as if they would protect it – given biblical accounts of those who dared touch it inappropriately, it is clear that not touching the ark was vital to life. Only those sanctified, set apart to carry it, could do so if they strictly followed all the regulations. Second, that as the priests carrying it on poles went into the shallow edges of the river Jordan, until the ark was above the waters and their feet were all in the waters, then the nation behind (probably being somewhat elevated above the river bank) would all see the miracle of God stopping the waters and making a passageway to cross over.
You also ask for a spiritual allusion to this matter of following Jesus Christ in one’s own pilgrimage. I can only think that as Jesus is the Way, and the Truth, and the Life (John 14:6), our eyes must be fixed on him, as the author and perfecter of faith (Hebrews 12:2). Not to keep following Jesus is to be misled and to wander astray. Yet a respectful distance is appropriate, for he has gone before us into heaven itself, while we still sojourn down here on earth. Thus, faith is needed to follow Jesus, even into the waters that appear to keep us from the ‘other side’, ‘Beulah’s land’. Sadly, many would direct people to ‘crossing over points’ that are simply not of God. Only the risen Christ can lead to the exact point where the waters will not overwhelm but, conversely, part. We do not need to be physically close to Christ to be protected by him, but spiritually close, using eyes of faith to see him, and being obedient to his directions as to the way we are to walk - Isaiah 30:21.