The differences between the two parts of the psalm seem so fundamental that the question arises: can this psalm indeed be viewed as a single unit?
The first half of Psalm 27 expresses a religious position of absolute trust in God, untainted by doubt. The psalmist is aware of the existence of enemies and foes, planning evil against him and quite capable of drawing near to consume his flesh; he anticipates the possibility of war being waged against him, and voices concern over a day of evil in the future. Nevertheless, none of this undermines in any way his complete trust in God to save him from his enemies. He concludes in a manner quite befitting the general atmosphere that prevails over this half of the psalm, envisioning his offerings in God's Temple as a gesture of thanks for his deliverance, with song and praise to God.
While the first half concludes on a triumphant note of joy, with praise to God for His deliverance, the second half begins with a cry to God by a psalmist in distress, uncertain as to God's response to him: "Hear, O Lord, my voice as I cry out; be gracious to me and answer me." This feeling continues throughout this half; a person does not plead, "Do not hide Your face from me" unless he feels that God is indeed hidden from him. Moreover, the psalmist fears God's anger, which may divert him from his path, and asks, "Do not divert your servant in (Your) anger."
It would seem that what we seek for our psalm is not a harmonistic solution, but rather an understanding of its duality as an expression of the duality that characterizes man's stance before God. In every person's life, there are situations in which the appropriate religious position is expressed in the first half, while there are other situations that are more accurately expressed in the second half. The order of the High Holy Days is such that Rosh Ha-shana – reflecting the idea that "the Lord is my Light" – is followed by Yom Kippur, with its fasting and confession. Likewise, it is proper that every individual sets off on his life's journey with the illumination of God's closeness, with confidence and joy. Only later on does he discover the other aspect of his position before God – the state that demands urgent supplication to God in order to overcome the feeling that God is hidden from him.