A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 27:1With a general strain of confidence, hope, and joy, especially in God's worship, in the midst of dangers, the Psalmist introduces prayer for divine help and guidance. (Psa 27:1-14)
light--is a common figure for comfort.
strength--or, "stronghold"--affording security against all violence. The interrogations give greater vividness to the negation implied.
psa 27:2eat . . . my flesh-- (Job 19:22; Psa 14:4). The allusion to wild beasts illustrates their rapacity.
they stumbled--"they" is emphatic; not I, but they were destroyed.
psa 27:3In the greatest dangers.
in this--that is, then, in such extremity.
psa 27:4The secret of his confidence is his delight in communion with God (Psa 16:11; Psa 23:6), beholding the harmony of His perfections, and seeking His favor in His temple or palace; a term applicable to the tabernacle (compare Psa 5:7). There he is safe (Psa 31:21; Psa 61:5). The figure is changed in the last clause, but the sentiment is the same.
psa 27:6head be lifted up--I shall be placed beyond the reach of my enemies. Hence he avows his purpose of rendering joyful thank offerings.
psa 27:7Still pressing need extorts prayer for help.
cry with my voice--denotes earnestness. Other things equal, Christians in earnest pray audibly, even in secret.
psa 27:8The meaning is clear, though the construction in a literal translation is obscure. The English Version supplies the implied clause. To seek God's face is to seek His favor (Psa 105:4).
psa 27:9Hide not, &c.-- (Psa 4:6; Psa 22:24). Against rejection he pleads former mercy and love.
psa 27:10In the extremity of earthly destitution (Psa 31:11; Psa 38:11), God provides (compare Mat 25:35).
psa 27:11thy way--of providence.
a plain path-- (Psa 26:12).
enemies--literally, "watchers for my fall" (Psa 5:8).
psa 27:12will--literally, "soul," "desire" (Psa 35:25).
enemies--literally, "oppressors." Falsehood aids cruelty against him.
breathe out--as being filled with it (Act 9:1).
psa 27:13The strong emotion is indicated by the incomplete sentence, for which the English Version supplies a proper clause; or, omitting that, and rendering, "yet I believed," &c., the contrast of his faith and his danger is expressed.
to see--is to experience (Psa 22:17).
psa 27:14Wait, &c.--in confident expectation. The last clause is, literally, "and wait," &c., as if expecting new measures of help.