Every verse starts with the Hebrew letter sadhe.
The psalmist acknowledged YHWH as being righteous or just and that all of his judgments were upright. Intrinsically just, the Most High never deviates from the ultimate standard of justice.
God commanded his “testimonies” or solemn charges in righteousness and abundant “faithfulness” or “truth” (LXX). The expression of God’s will has the force of a command. As issuing from him (the ultimate standard of righteousness and abundant faithfulness or dependability of the highest degree), the solemn charges serving as a guide for upright conduct are right or just and completely trustworthy.
In verse 139, the Masoretic Text does not identify the object of the psalmist’s zeal. Rahlfs’ text of the Septuagint reads, “zeal for your house.” Another reading of the Greek text is “zeal for you [God].” So intense was the psalmist’s zeal that he spoke of it as putting an end to him or, according to the Septuagint, wasting him away. His consuming zeal was aroused because of seeing his enemies forgetting or ignoring YHWH’s words.
God’s word or promise, everything that is an expression of his wishes and will, is pure as if having been subjected to a refiner’s fire. As God’s servant, the psalmist loved that word, trusting it fully in distressing times.
Others regarded the psalmist as insignificant (like a mere youth) and despised him, contemptuously looking down upon him. This did not, however, cause him to change his course. He did not “forget” God’s precepts but always kept them in mind, conducting himself according to the guidance they provided.
YHWH’s righteousness or justice never changes. It remains unalterable righteousness for all time to come. God’s law is “truth,” completely trustworthy or dependable as a guide.
Even though the psalmist experienced distress and anguish, he still found delight in God’s commandments. It brought him joy to live in harmony with them. According to the Septuagint, the commandments were the object of his meditation.
God’s testimonies or solemn charges are “righteous,” just, or right, continuing to be such for all time to come. For the psalmist, life meant more than merely existing. He wanted his life to be properly guided. Therefore, he prayed for understanding or discernment, earnestly desiring to know God’s ways and then living in the real sense of the word as one who conducted himself uprightly.