This is a continuation of one Psalm (42-43 combined).
The godly remnant calls on God to act on their behalf. The deceitful man is the Antichrist (TTB).
v.1-2 The psalmist asks for vindication from a deceitful man.
v.3-4 “Send out your light and truth” (and let them lead me)
Jesus said: “I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.” (John 8:12)
v.5 refrain
5 Why are you cast down, O my soul,
and why are you in turmoil within me?
Hope in God; for I shall again praise him,
my salvation and my God.