As a conclusion to the negative instruction we have the more positive conclusion that the Father knows what we need. This is an important concept, but before discussing it we should understand how it is a conclusion to the prayer of the heathen. The prayer of the heathen is designed to get something from their god. The prayer of the heathen was considered to be magically effective and binding if it was done correctly. Thus the human decided what they needed, and pushed that need to the gods for solution in just the way that the human had decided.
Jesus reverses this view of how prayer works. Not only is prayer not a way to bind God, it is simply our petition to God to have God work in our favor as he already knows we need. The directionality of the need fulfillment is reversed. We do not decide what we need and require it of the gods as do the heathen, but we petition God to act in our favor, which He will do because He knows what is really in our favor.
Social Context: In the world and among the people to whom Jesus spoke, there was great need to understand that God could be acting in their interests even when He did not fulfill their wants. As a people, Israel wanted to throw off the Roman domination. As a segment of society, the poor wanted to throw off the domination of their overlords and those to whom they were indebted. They wanted many things that were not forthcoming. They had prayers unanswered. Where was God in this process? It was important for them to realize that there was a God who answered prayers, but answered them according to the spiritual needs of the person, not the material ones. This was a God who understood what they truly needed in their spirits and provided that, even while their prayers for deliverance for earthly problems did not appear to be effective. God gives us what we need, not what we want.
Textual: There are no changes from the Matthean text.