Psalms 3:3

But thou, O Lord, art a shield for me - Not only in these dangers, but in all dangers. The declaration here has a general form, as if he could trust in him at all times. It shows what his feelings were on the occasion here referred to, when dangers stood thick around him, and what his feelings habitually were in times of peril. The shield was a well-known part of ancient armor, of use, according to the ancient modes of warfare, when swords, and spears, and arrows were employed, but of use only then, since they would constitute no defense against a musket or cannonball. They were usually made of tough and thick hides, fastened to a rim, and so attached to the left arm that they could be readily thrown before the body when attacked, or so that, as they were usually held, the vital parts of the body would be protected. See the notes at Ephesians 6:14-16. From this use of the shield it was natural to speak of God as the “shield,” or the “Protector” of his people - an appellation which is often given to him in the Scriptures (Genesis 15:1; Deu 33:29; 2 Samuel 22:3; Psalms 28:7; Psalms 119:114; Psalms 144:2; Psalms 33:20; Psalms 84:11; Proverbs 30:5.

My glory - My honor, or the source of my honor. That is, he bestows upon me all the honor that I have, and it is my glory that I may put my trust in him. I regard it as an honor to be permitted, in times of danger and trouble, to rely on him - a sentiment in which every true child of God will unite.

And the lifter up of my head - The head, in time of trouble and sorrow is naturally bowed down, as if overpowered with the weight of affliction. See Psalms 35:14 : “I bowed down heavily as one that mourneth for his mother;” Psalms 38:6 : “I am bowed down greatly; I go mourning all the day.” Compare Psalms 42:5; Psalms 44:25; Psalms 57:6; John 19:30. To lift up the head, therefore, or to raise one up, is to relieve his distresses, or to take away his troubles. Such a helper, David says, he had always found God to be, and he looks to him as one who is able to help him still. That is, he feels that God can so entirely take away his present griefs as to reinstate him in his former happy and honorable condition.