"Giving Back"

I wonder what the implication is when someone says they are doing volunteer work or donating money or helping someone directly because they want to "give back." 

Is the implication that they have taken something and want to give back some of it or all of it or is it that they have been given something and now want to give some or all of it back? 

Is "giving back" different from giving forward to someone never before encountered? 

Is there some suggestion in a person's declaration of intent to begin "giving back" that nothing much has been given in the past but that a point in life has been reached at which "giving back" is appropriate and affordable and not too disruptive or maybe even fun or ego building or image enhancing? 

I think it is the simple word "back" that bothers me about this popular phrase probably because of the suggestion of reciprocity.  After all, Jesus is not reported in Acts 20:35 to have said, "It is more blessed to give (back) than to receive," and while there may be some suggestion of reciprocity in Matthew 10:8, "Freely you have received, freely give," the word "freely" seems to take away the selfishness.

Of course we know that Jesus gave everything so the standard has been established.  If only I...
 
When he had received the drink, Jesus said, "It is finished." With that, he bowed his head and gave up his spirit. - John 19:30

Sorry for the rant about a pet peeve.  But it is food for thought.