A few sermon notes from one of the ministers.
Psalm 43 v 3;4. "O send out thy light and thy truth: let them lead me; let them bring me unto thy holy hill, and to thy tabernacles. 4 Then will I go unto the altar of God, unto God my exceeding joy: yea, upon the harp will I praise thee, O God my God".
The desire is for a blessing on God's Word to his own soul, for the Word to be his guide. The first word in v3 is 'O'…how much meaning is in that one-vowel word of longing, which also appears at the end of v4. The psalmist is able to say that the Most High is "my God".