The true essence of bringing an offering to God has never been about the physical act of sacrificing an animal. Instead, it is a process of internal transformation, demanding sincerity and moral wholeness. A relationship with God is built on refining one's character and keeping one's word, rather than attempting to fulfill any supposed divine needs. Sacrifices offer no benefit to God; they exist entirely for the betterment of humanity [אבן עזרא].
The primary approach among commentators is that the concept of thanksgiving actually refers to the act of confession. The most desirable offering is brought when a person confesses their sins, feels genuine regret, and commits to never repeating those mistakes. When bringing an animal, a person must approach with a broken spirit, realizing that because of their actions, they themselves deserved to die, and the animal merely serves as a substitute [מצודת דוד, אלשיך]. Without this internal process of confession and repentance, the physical act of bringing an offering is completely useless [מאירי]. Taking a slightly different approach, [אבן עזרא] maintains that the focus is on the actual thanksgiving offering. He notes that bringing an offering of gratitude, combined with careful observance of the Torah, is actually more desirable than bringing an offering that is completely burned on the altar. Adding a deeper layer to the concept of gratitude, [אלשיך] emphasizes that the divine attribute of strict justice is central to this process. Therefore, a person is encouraged to bring a thanksgiving offering even when experiencing pain and suffering, recognizing that these hardships are also a gift from God.
Alongside gratitude, there is a strict obligation to fulfill any vows a person makes to honor God [ביאור שטיינזלץ]. Even though God does not need these offerings, the requirement to pay them is designed to train a person to be careful with their words. If people are expected to keep their promises to flesh and blood, they must certainly do so for the Most High God, from whom no one can hide or escape [רד״ק]. Despite this obligation, commentators agree that it is generally better to avoid making vows altogether [רד״ק, מצודת דוד]. Making a vow is truly appropriate only during times of deep distress, when a person feels that God is distant and removed, prompting them to reach out to Him as the Most High [אלשיך].
Ultimately, these actions are deeply intertwined. A person can only properly fulfill their vows after they have first confessed their wrongs and completely repented. Only through this sincere internal repair will their offerings be gladly accepted by God [רש״י].