In the footsteps of God, as the disciples of Jesus you are good to people from whom you will not receive anything good in return. God’s vertical disinterested love propagates this goodness. This verse says Christians do good unto those who have not done so for Christians, and of whom you should not expect them to do so. In this way you show the selflessness of heavenly love, and this is in distinction to “sinners,” namely those who live without wanting to know God.
33 Si vous faites du bien à ceux qui vous font du bien, quel gré vous en saura-t-on? Les pécheurs aussi agissent de même.