This psalm also is entitled "A Song of Degrees." See the notes at Introduction to Psalm 120:1-7. The author and the occasion on which it was composed are unknown, as is also the reason why it was included in this group of psalms.
The language of the psalm seems to be that of an individual; but most interpreters suppose that it is an individual speaking in the name of the nation, and representing its calamities and its penitence. Some have imagined that the person represented as speaking in Psalm 130:7-8, is a different individual from the one speaking in the other part of the psalm, but there seems to be no ground for this opinion. It is commonly supposed that the psalm had reference to the state of the Jews in the Babylonian captivity, but there is no necessity for limiting it to that period, if indeed it has any reference to the people of Israel. There were many occasions in their history when the language of the psalm would not be less appropriate than at that time. But there is no necessity at all for supposing that it refers to the nation as such. It may be the language of an individual, mourning over his sins, and pleading for mercy, expressing deep conviction of sin, and humble trust in God as the only hope for a convinced, condemned, and penitent sinner. As such, it would represent what has occurred in thousands of cases when sinners have been brought to conviction of sin, and have cried for mercy. Understood in this manner, it is one of the most instructive and touching of the psalms. I know of no reason why it may not be so regarded.

The prayer of a penitent to God, with confession of sin, Psalm 130:1-3. Confidence in God's mercy, and waiting upon him, Psalm 130:4-6. Israel is encouraged to hope in the Lord, because of his willingness to save, Psalm 130:7, Psalm 130:8.
This Psalm has no title nor author's name, either in the Hebrew, or in any of the Versions; though the Syriac says it was spoken of Nehemiah the priest. It was most probably composed during the captivity; and contains the complaint of the afflicted Jews, with their hopes of the remission of those sins which were the cause of their sufferings, and their restoration from captivity to their own land. This is one of those called penitential Psalm.

INTRODUCTION TO PSALM 130
A Song of degrees. This psalm is by some thought to have been written by David either when persecuted by Saul, and in great distress, and fearful he should perish by him; or else when in great distress of mind because of sin, after the affair of Bathsheba; and it is reckoned therefore among the penitential psalms. Though others think it was written by Ezra, or some other godly person in the captivity; and Aben Ezra and R. Obadiah interpret it of Israel in captivity. The Syriac inscription is,
"one of the psalms of ascension: it is said concerning Nehemiah the priest (or rather the prince or governor, since Nehemiah was no priest); and it intimates in it the prayer of the martyrs.''
It may be applied to any person in distress, outward or inward; applying to God for help and deliverance, for pardoning grace and mercy; encouraging himself and others to hope for it.

(Psalm 130:1-4) The psalmist's hope in prayer.
(Psalm 130:5-8) His patience in hope.

De Profundis
Luther, being once asked which were the best Psalm, replied, Psalmi Paulini; and when his companions at table pressed him to say which these were, he answered: Psalm 32:1-11; Ps 51; Psalm 130:1-8, and Psalm 143:1-12. In fact in Psalm 130:1-8 the condemnability of the natural man, the freeness of mercy, and the spiritual nature of redemption are expressed in a manner thoroughly Pauline. It is the sixth among the seven Psalmi poenitentiales (Psalm 6:1-10, Psalm 32:1-11, Ps 38, Ps 51, Ps 102, Psalm 130:1-8, Psalm 143:1-12).
Even the chronicler had this Psalm before him in the present classification, which puts it near to Ps 132; for the independent addition with which he enriches Solomon's prayer at the dedication of the Temple, 2-Chronicles 6:40-42, is compiled out of passages of Psalm 130:1-8 (Psalm 130:2, cf. the divine response, 2-Chronicles 7:15) and Ps 132 (Psalm 132:8, Psalm 132:16, Psalm 132:10).
The mutual relation of Psalm 130:1-8 to Ps 86 has been already noticed there. The two Psalm are first attempts at adding a third, Adonajic style to the Jehovic and Elohimic Psalm-style. There Adonaj is repeated seven times, and three times in this Psalm. There are also other indications that the writer of Psalm 130:1-8 was acquainted with that Ps 86 (compare Psalm 130:2, שׁמעה בקולי, with Psalm 86:6, והקשׁיבה בּקול; Psalm 130:2, לקול תּחנוּני, with Psalm 86:6, בּקול תּחנוּנותי; Psalm 130:4, עמּך הסּליחה, with Psalm 86:5, וסלּח; Psalm 130:8, החסד עם ה/ הח, with Psalm 86:5, Psalm 86:15, רב־חסד). The fact that קשּׁוּב (after the form שׁכּוּל), occurs besides only in those dependent passages of the chronicler, and קשּׁב only in Nehemiah 1:6, Nehemiah 1:11, as סליחה besides only in Daniel 9:9; Nehemiah 9:17, brings our Psalm down into a later period of the language; and moreover Ps 86 is not Davidic.