Saint Vincent de Paul described the poor whom he helped as his masters. Therefore, he served them.

We understood that we must see not only the poor as our masters, but also every neighbor. In fact, if Jesus said that He did not come to be served but to serve (and we must be able to say the same of ourselves), it means that we are the servant and the others are the masters.
Thus, the other person, our neighbor, is the one who must have the first word, who must be honored and obeyed because he or she is the one who commands.

Well then, what attitude should we have towards our neighbors?
We should give them the possibility of taking the first step, of taking the initiative. We could say: of being the first to love.

For this to happen, we need to put ourselves at their disposal and approach the other completely empty of ourselves. We need to put aside even our greatest and most beautiful ‘possessions’ for them. [ . . . ] 
In this way, our neighbor can express himself or herself, because he or she finds someone who welcomes and accepts them: they are able to give of themselves.

But since the "nothing" within us is a "nothingness of love" -- which is certainly not the same as inexistence -- the Holy Spirit, attentively present within us, can enlighten us. The Spirit allows us, in a certain sense, to help guide the conversation so that our neighbor can fully open himself or herself. Not only, but the Holy Spirit enables us to perceive the ‘life’ present and ‘living’ in our neighbor’s heart, the small flame of the divine in him or her, at a profoundly spiritual level; or ‘alive’ in the sense of those fundamental human values placed by the Lord in every soul at creation.

By serving others with infinite discretion, we gently and lovingly engraft aspects of the truth, of the gospel message dwelling within ourselves. This brings fullness and completeness to what our neighbor already believes and for which he or she is often awaiting and even yearning for: aspects that in themselves carry the whole of the truth.