"But thou, O LORD, art a shield for me; my glory, and the lifter up of mine head" (Psa 3:3) .
When people walk, they are supposed to have their heads up and their eyes forward. They should be able to admire the surroundings they pass through. Greet the people they meet with smiles and experience life and not just drift by anonymously.
A bowed head when walking is usually a sign of shame. To put one's face down when walking is usually a sign of lack of self confidence or a feeling of inferiority and low self-esteem. This is both literally and figuratively. It is a sign of defeat. Whenever people are defeated, the first thing they do is put their face to the ground and then walk away without lifting their head. I have seen these scenario multiple times. That's why I can relate strongly when David said that God is the lifter of our head.
Imagine that you are in a position where you never have to put your head down again in shame or defeat! That is what God means to us. The Bible said "He himself bore our sin" (1 Pet 2:24). The word sin also means wrongdoings. That means whatever you may have done wrong in the past, that brought shame upon you. God has taken it away. And has lifted your head! You are free!