to gather: to bring scattered people or things together into one place
This is the everyday core of the word. Something that was spread out or apart is brought together: an army mustered for battle, a crowd called to one spot, a flock driven in, possessions pulled together. The same word covers both the people who do the gathering and the people who are gathered, so it often appears in a form that means the crowd assembled or the troops came together.
From this physical sense the word naturally stretches to the work of harvest. Bringing in a crop is simply gathering what the field has produced before it is lost, so the autumn harvest festival was called the feast of ingathering. The same idea sits behind taking in a stray animal or a homeless traveler: you bring them in off the open and under your own roof.
What ties this whole range together is movement from scattered to collected, from outside to inside, from many places to one. The word says nothing on its own about why things are gathered or what happens next; the surrounding text supplies that.