The mariners' rowing is somewhat ragged at the beginning of the poem, as they have to deal with a large tidal wave coming towards them. Conditions at sea are clearly bad, but the captain of the ship attempts to raise the morale of his men by telling that the wave will roll them shoreward soon. The old sea dog clearly knows from personal experience that a large wave can be a blessing as well as a curse. Not only can it destroy a ship, hurtling its crew into the briny depths, it can also lift a ship upon its giant crest before depositing it safely on dry land.
And that's what happens here. For by the afternoon, the ship's crew have fetched up on a strange land where it always seems like afternoon. This is the idyllic, beguiling land of the lotos-eaters, that strange race of people who live in a kind of carefree, aesthetic dreamworld free from the troubles and struggles that the mariners experience on a daily basis.
Having landed here, the mariners are presented with a dilemma. At some point, they must decide whether they wish to stay among this lush, dreamy landscape and rest from weariness or head off back out to sea at the earliest opportunity.