Hester suggests that Dimmesdale flee the community, either by boarding a ship or wandering further into the interior, anywhere where Chillingworth cannot get to him. By leaving he could perchance reestablish himself and preach to the "red men." Both Hester and Dimmesdale realize that his will to live, his spirit continues to be eroded by his contact with Chillingworth, and his physical and mental health continue to falter. Hester even volunteers to flee with him, to be his support. Sadly, this phrasing is a bit of foreshadowing, as the minister never leaves the village, and does, in fact, lie down and die at his confession.
These lines are spoken in Chapter 17. Hester is the one who speaks them and she says them to Dimmesdale.
What she is doing is trying to get him to snap out of the depression he is in. Dimmesdale has been depressed because of his sin and because Chillingworth is hounding him about it. It has been about seven years since the beginning of the book and Dimmesdale is in pretty poor physical and mental health.
So at the point these lines are spoken, Hester is pretty much telling him that he needs to just do something, anything. Stop moping around and go do something.