Can I believe?

What is the difference between a shield and a buckler?
Sometimes we quote, The Lord is our shield and buckler.

But seriously, what does a shield do? And what is the function of a buckler?
I came across an interesting article about the difference here:
http://www.thortrains.com/getright/drillbuckler.htm

The author states:

"The shield does not stand passively on the soldier's left arm.  It is an active part of his kit, and he uses it with purpose.  He will hold his shield forward, ready to move it in any direction.  He will look to block an enemy's weapon in such a way as to create an opening for a strike. When the soldier attacks, he will position his shield to reduce his own vulnerability.  You can be certain that the shield will always be poised between himself and the enemy. 

The soldier does not stick his shield out stiffly.  It is a fluid thing, moving with him.

The buckler is a small shield, used mainly to deflect, trap and strike.  While it is useful for duels and small fights, it is not good for large-scale battle.  Bucklers are not good for handling arrows or other large projectiles.  These little shields were mostly carried by individuals who might have to defend themselves in day to day situations.  Granted, they gained tactical importance for a short time during the era of pike and musket warfare. However, they were a civilian weapon."

With the above understanding,  

The shield is always poised between the soldier and his enemy.  It is a fluid thing, moving with him. 

The buckler, is a small shield, carried by individuals who might have to defend themselves in day to day situations. 

With the above understanding in mind, what imagery comes to mind when we read Psalm 18:2

The LORD is my rock, and my fortress, and my deliverer; my God, my strength, in whom I will trust; my buckler, and the horn of my salvation, and my high tower.
(Read more about "horn or salvation" at http://www.oxfordbiblicalstudies.com/article/opr/t94/e898 )

And how marvelous an understanding David had of the LORD God that he acknowledges how completely helpless he was, and how completely dependent his life was in the hands of the Lord, yet with a resolute trust in the Lord's absolute desire and ability to protect him, and to be with him (as a buckler) in every day's seemingly daily ongoings.

How now shall we read this promise in Matthew 28:20b:
"and lo, I am with you always, even to the end of the age."

Will we believe Him enough forsake our fears of betrayal and abandonment? What does it mean that He is always with us? It is not a suggestion. He who promised is faithful.  Will I now embrace this truth, instead of rejecting Him?