Psalm 38:18, "For I will declare my iniquity; I will be sorry for my sin," expresses a profound moment of acknowledgment, confession, and genuine remorse. Let's break it down:

"For I will declare my iniquity": This means the speaker is committing to honestly admitting their wrongdoing. They're not hiding it, denying it, or making excuses. They're being upfront about their "iniquity" (which refers to wickedness, injustice, or moral wrong). "Declare" implies a clear and open confession, not a mumbled admission.

"I will be sorry for my sin": This goes beyond simply admitting guilt. It shows a deep sense of regret and contrition. The speaker isn't just acknowledging they did something wrong; they are truly grieved by it. "Sorry" in this context means genuine remorse, a feeling of pain and distress over having sinned.

In essence, the verse conveys:

Humility: The speaker is humbling themselves before God (or whoever they're addressing) by acknowledging their faults.
Repentance: It's a step towards repentance. Confession and remorse are essential components of turning away from sin.
Sorrow for Offending: The speaker is not only sorry for the consequences of their sin but also for the fact that they offended God or violated moral principles.
Desire for Forgiveness: Implicitly, there's an underlying desire for forgiveness and restoration. People usually confess sin when they hope to be cleansed from it.

The context of Psalm 38: It's important to note that Psalm 38 is a lament, a prayer expressing deep sorrow and distress. The speaker is suffering physically and emotionally, and they attribute some of their suffering to their sin. Confessing their sin and expressing remorse is likely a way for them to seek God's mercy and healing.

In short, the verse is a powerful expression of honesty, regret, and a desire to make amends for past wrongdoing. It's a cornerstone of repentance and a vital step in seeking forgiveness and reconciliation.