While the psalmist was enjoying God in His house and His city, a lot of things came into his thoughts to distract him. That constituted a kind of sentiment, which he poured out in his expressions. Psalm 43:1-2 shows us the mixed expressions of the psalmist's sentiment in his enjoyment of God in His house and city.
To pant after God and to thirst for God are marvelous, wonderful, and good. In this we should remain, but we lack control. Thoughts come in as darts to distract us. These thoughts constitute our sentiment, which we utter in expressions. Mixed expressions such as these are the contents of many of the psalms.
The psalmist asked God to give him light and truth that would lead him and bring him to God's holy mountain and to His tabernacles that he might go to the altar of God, to the God of his exultation's rejoicing (43:3-4). This means that he was away from the holy mountain and from the temple. He asked God to send forth light and truth. When we have light and truth, we have the way, but at that time the people of Israel did not have a way to get out of their captivity. They did not have the way, the leading, to get back to Mount Zion, the holy mountain, so that they could return to God's house.
The psalmists who wrote Psalms 42—44 were really lovers of God. They were panting after God, thirsting for God, and desiring to go back to Jerusalem, to get to Mount Zion to reach the altar. Then they could enter into the temple to meet the God of their exultation's rejoicing. This is why they prayed that God would give them the light and the truth that they might know how to get out of their captivity and get back to God's dwelling place.