I will open my mouth in a parable - See the notes at Psalm 49:4. The word "parable" here means a statement by analogy or comparison; that is, he would bring out what he had to say by a course of reasoning founded on an analogy drawn from the ancient history of the people.
I will utter dark sayings of old - Of ancient times; that is, maxims, or sententious thoughts, which had come down from past times, and which embodied the results of ancient observation and reflection. Compare Psalm 49:4, where the word rendered "dark sayings" is explained. He would bring out, and apply, to the present case, the maxims of ancient wisdom.

In a parable - Or, I will give you instruction by numerous examples; see Psalm 49:1-4 (note), which bears a great similarity to this; and see the notes there. The term parable, in its various acceptations, has already been sufficiently explained; but משל mashal may here mean example, as opposed to תורה torah, law or precept, Psalm 49:1.

I will open my mouth,.... Speak freely, boldly, and without reserve, Ephesians 6:19, so Christ opened his mouth, Matthew 5:2,
in a parable; not that what follows in this psalm was such, but what were delivered by our Lord in the days of his flesh, who spake many parables; as of the sower, and of tares, and of the grain of mustard seed, and many others, and without a parable he spake not, and so fulfilled what he here said he would do, Matthew 13:34.
I will utter dark sayings of old; sayings that relate to things of old; meaning not to the coming of the children of Israel out of Egypt, and what follows in the psalm, delivered, as Aben Ezra and Kimchi observe, in figurative and topical terms, as in Psalm 78:19, but to the things which were from the foundation of the world, as the phrase is rendered in Matthew 13:35, spoken of Christ in his ministry, such as the fall of the angels, the ruin of man by Satan, the murder of Abel, Abraham's sight of his day with joy, and many things that were said by them of old, Luke 10:18 or rather this refers to the Gospel, and the sayings and doctrines of it, which were kept secret since the world began, Matthew 13:3, yea, which were ordained before the world was, and therefore called the everlasting Gospel, 1-Corinthians 2:7 and here in the Arabic version, "eternal mysteries"; such as concerning the everlasting love of God to his people, his everlasting choice of them, and everlasting covenant with them: and the sayings or doctrines of the Gospel may he called "dark", because secret, hidden, and mysterious; and were so under the legal dispensation, in comparison of the more clear light under the Gospel dispensation; they having been wrapped up in types and shadows, and in the rites and ceremonies of the law, but now held forth clearly and plainly in the ministry of Christ and his apostles, as in a glass: these Christ says he would "utter" or deliver out as water from a fountain, in great plenty, as he did; he came in the fulness of the blessing of the Gospel; and being full of grace and truth, the doctrines of grace and truth, these came by him, and were delivered from him in all their fulness and glory.

Parable - Weighty sentences. Dark sayings - Not that the words are hard to be understood, but the things, God's transcendent goodness, their unparallel'd ingratitude; and their stupid ignorance and insensibleness, under such excellent teachings of God's word and works, are prodigious and hard to be believed. Of old - Of things done in ancient times.