Psalm 43:3-5

"Oh, send Your light and Your truth! Let them lead me; Let them bring me to Your holy hill and to Your tabernacle [dwelling places]. Then I will go to the altar of God, to God my exceeding joy; and on the harp I will praise You, O God, my God.

Why are you cast down, O my soul? And why are you disquieted within me? Hope in God; for I shall yet praise Him, the help [salvation] of my countenance and my God." (nkjv)

"Give me your lantern and compass,

give me a map,

So I can find my way to the sacred mountain,

to the place of your presence,

To enter the place of worship, meet my exuberant God,

Sing my thanks with a harp,

magnificent God, my God.

Why are you down in the dumps, dear soul?

Why are you crying the blues?

Fix my eyes on God--soon I'll be praising again.

He puts a smile on my face.

He's my God." (msg)

One commentary I read said this about the aspects of light and truth in this Psalm:

"Light and truth. Delightful and all comprehensive words. Thy contain all the salvation and all the desire of a believing, confiding soul. But it is only when thus combined -- separated they are no longer a ground of trust and joy. For what would favour avail without faithfulness? It would be no more than the uncertain friendship of men, who smile today and reproach tomorrow; who make large promises, but do not perform them. Even the light which angels and glorified spirits enjoy in heaven would be insufficient to banish all fear and to fill them with satisfaction, were it not for their confidence in the truth of God. How much more, then, must this be the case with erring, sinful, mortals on earth? When the humble spirit is bowed down under a sense of its utter unworthiness and innumerable weaknesses and defilements, its negligences, follies, and wanderings, what should save from despair but the confidence that he who has been merciful will also be faithful; that God is truth as well as light; that he hath said, "I will never leave thee nor forsake thee;" that he "cannot lie," and that, therefore, "his mercy endureth for ever?" On the other hand, truth without light, faithfulness without grace, would be only the dreadful execution of terrible but just denunciations on the transgressors of the holy law. "In the day that thou eatest thereof thou shalt surely die." Adam ate, and in that day became the subject of sin and death. This was truth executing judgment. But light arose around the darkness; beams of mercy tempered the heavy cloud. The promise of the Great Deliverer was given; then faithfulness was enlisted on the side of grace, and became engaged for its bestowment; "mercy and truth met together; righteousness and peace kissed each other." Since then, all humble and trusting souls have beheld them united, and have made their union the ground of their confidence and joy. "