Bible Commentary
1 God is a light to his people, to show them the way when they are in doubt, to comfort and rejoice their hearts when they are in sorrow. "He is my salvation, in whom I am safe and by whom I shall be saved.’’ "He is the strength of my life, not only the protector of my exposed life, who keeps me from being slain, but the strength of my frail weak life, who keeps me from fainting, sinking, and dying away.’’²
2 The psalmist had many enemies, they were of different sorts, but they were unanimous in mischief and hearty in hatred. They advanced to the attack, leaping upon the victim like a lion upon its prey. Like cannibals they would make a full end of the man, tear him limb from limb, and make a feast for their malice.  However God's breath blew them off their legs. There were stones in the way which they never reckoned upon, and over these they made an ignominious tumble.³
3 "Though they be numerous, a host of them,—though they be daring and their attempts threatening,—though they encamp against me, an army against one man,—though they wage war upon me, yet my heart shall not fear.’’ Hosts cannot hurt us if the Lord of hosts protect us.²
4 David's longing to be engaged perpetually in the service of God, to be a perpetual guest of the heavenly Host, is beautifully expressed in this psalm.  At the Christian sanctuary our minds are enlightened, our doubts removed, and our hearts comforted by God's truth.⁴
5 The safety of believers is not in the walls of the temple, but in the God of the temple and their comfort in communion with him.² The man whom God himself sets on high above his foes, is like an impregnable rock which never can be stormed! ³
6 Godly men of old prayed in faith, nothing wavering, and spoke of their answer to their prayers as a certainty. David was by faith so sure of a glorious victory over all those who beset him, that he arranged in his own heart what he would do when his foes lay all prostrate before him.³  Whatever is the matter of our joy ought to be the matter of our praise; and, when we attend upon God in holy ordinances, we ought to be much in joy and praise. It is for the glory of our God that we should sing in his ways; and, whenever God lifts us up above our enemies, we ought to exalt him in our praises.²
7 At this point in the psalm there is a complete change in tone from implicit trust to a plaintive cry for help.  This change brings one school of critics to the conclusion that the psalm is really composed of two separate psalms.  Such a conclusion is not at all necessary when one grants that, despite the psalmist's confidence in God, the force of actual circumstances induces him to cry to God for help in a very real world.  Even when assured of God's favor, we need continually to recognize our need of Him and to request His aid.⁴
8 This verse is the dialogue of a beautiful fellowship between David and his God.  God had said to him: "Seek ye my face."  David reminds God of His command, and from the depths of his heart replies, "I will seek thy face."  Here is intimacy indeed, resembling the friendship that existed between Moses and God. Precious is that fellowship with God which, in time of need, finds the soul speaking to itself the counsel of God.⁴
9 Other servants had been put away when they proved unfaithful, as for instance, his predecessor Saul; and this made David, while conscious of many faults, most anxious that divine long suffering should continue him in favour. The first petition, "leave me not," may refer to temporary desertions, and the second word to the final withdrawal of grace, both are to be prayed against.³
10 Some of the greatest of the saints have been cast out by their families, and persecuted for righteousness' sake. Then the Lord will espouse my cause, will uplift me from my woes, will carry me in his arms, will elevate me above my enemies, will at last receive me to his eternal dwelling place.³
11 Plainness or downright honesty will direct us into and keep us in the way of our duty. The psalmist begs to be guided in a plain path, because of his enemies, or (as the margin reads it) his observers. His enemies watched for his halting, that they may find occasion against him. Saul eyed David, 1 Sa. 18:9. This quickened him to pray, "Lord, lead me in a plain path, that they may have nothing ill, or nothing that looks ill, to lay to my charge.’’²
12  The psalmist says deliver me not over unto the will of mine enemies; or I should be like a victim cast to the lions, to be rent in pieces and utterly devoured.³  Herein David was a type of Christ; for false witnesses rose up against him, and such as breathed out cruelty, thirsting after his blood. Though David may have been delivered into wicked hands of his enemies, he was not delivered over to their will, for they could not prevent his exaltation.²
13  The words "I had fainted" do not occur in the original.  They were inserted to complete the evident meaning of the psalmist: "What would have become of me, if I had not believed in the goodness of God!" So many and formidable are his enemies that he would collapse were it not for his sure belief that he will ultimately see a revelation of God's goodness on earth.⁴   
14  The psalmist is primarily exhorting himself.  His stronger self is encouraging his weaker nature not to despair.  The psalm closes with a repetition of the injunction: "Wait, I say, on the Lord," as if the psalmist would fix deep in our minds the idea that at all times of doubt and danger, instead of despairing, we should go forward "in the strength of the Lord God"⁴   

References and notes
1.  King James Authorized Version
2.  Matthew Henry Complete Commentary on the Whole Bible - http://bible.crosswalk.com/Commentaries
3. Charles H. Spurgeon, "The Treasury of David  - http://bible.crosswalk.com/Commentaries/TreasuryofDavid/
4. Seventh-day Adventist Bible Commentary Vol. 3 pgs 695 - 597
5. ChristadelphianBooksOnline George Booker Psalms Studies Book 1 - http://www.christadelphianbooks.org/booker/psalms1/