Of Plymouth Plantation is William Bradford's personal journal which was written over the course of about twenty years in the first half of the seventeenth century but was not published until the mid-1800s. It is the most significant contemporary account of the Pilgrims before, during, and after their landing at Plymouth.
The line to which you refer in your question is in part one of the journal, which covers the twelve years or so between the Pilgrims being forced to leave England and fleeing to Holland and their arrival in Plymouth. After they arrived, the sojourners fell upn the land and kissed it, thanking God for bringing them here safely. Then Bradford pauses in his narrative for a moment, as mentioned in your question. The actual quote reads this way:
But here I cannot but stay and make a pause, and stand half amazed at this poor people's present condition; and so I think will the reader, too, when he well considers the same. Being thus passed the vast ocean, and a sea of troubles before in their preparation (as may be remembered by that which went before), they had now no friends to welcome them nor inns to entertain or refresh their weatherbeaten bodies; no houses or much less towns to repair to, to seek for succor.
The phrase "But here I cannot but stay and make a pause" is a rather archaic (old-fashioned) and cumbersome way of saying "I need to stop at this point in the story" or "I cannot help but stop here in my story." He goes on to express his admiration for these Pilgrims who, having endured the troubles in England and Holland as well as the trials of the ocean crossing, are now in a place where there is nothing. They have no friends to greet them, no shelters or buildings in which to take refuge, and no place to go for rest or refreshing. In other words, before he continues his story, Bradford wants to stop and express his amazement at the resilience and endurance of these people.