"Take care that you do not despise one of these little ones; for, I tell you, in heaven their angels continually see the face of my Father in heaven."

To "continually see the face of the Father" constitutes the highest joy in heaven and is the primary activity of men and angels in heaven.  In that contemplative gaze is to be found all love, and from there all lesser actions flow.  Seek always, therefore, to keep your heart and mind directed solely toward God while engaged in your daily affairs.

If obedience to God's commands is not sufficient for you to respect, love and honor your littlest of brothers consider the staggering dignity which is theirs due to being assigned a heavenly companion who gazes on both God and their charge simultaneously.  With this in mind who would deliberately bear any improper attitude towards them?  Moreover you yourself have such an angel who continually sees the face of Christ's Father in heaven even while being with you at every moment.

Why does a man need such a thought as this to spur him on when we know that God himself sees all of our actions, knows all of our thoughts and is aware of the movements of our heart before they even occur?  I think it is because man is finite; he needs a concept of progression and hierarchy to help him understand the infinite.  In mathematics we have the number system which allows our minds to track from the very small to the exceedingly large and even progressions which stretch infinitely onward.  In astronomy we can appreciate the size of the earth, its distance to the sun, the size of the other planets, the size of our sun, the size of our solar system, our place in the galaxy, the immensity of the Milky Way and then on to other galaxies, galaxy clusters and so on, seemingly forever.  And thus between ourselves and God lies a vast hierarchy of angels which stretch between man's incredible feebleness and God's incomprehensible infinity of love, knowledge, goodness, oneness.  This helps the mind progress from almost nothingness up to the vastness of God.  Even though the fullness of God can surround a man, and a man in heaven can also gaze on God's face like his angel, this almost never ending progression of hierarchy seems necessary for the finite to understand the infinite.