9 Here the Hebrew expression כִּי־אִם (ki-’im, “instead”) introduces a contrast between the sinful behavior depicted in v. 1 and the godly lifestyle described in v. 2.
10 Heb “his delight [is] in the law of the Lord.” In light of the following line, which focuses on studying the Lord’s law, one might translate, “he finds pleasure in studying the Lord’s commands.” However, even if one translates the line this way, it is important to recognize that mere study and intellectual awareness are not ultimately what bring divine favor. Study of the law is metonymic here for the correct attitudes and behavior that should result from an awareness of and commitment to God’s moral will; thus “obeying” has been used in the translation rather than “studying.”
11 The Hebrew imperfect verbal form draws attention to the characteristic behavior described here and lends support to the hyperbolic adverbial phrase “day and night.” The verb הָגָה (hagag) means “to recite quietly; to meditate” and refers metonymically to intense study and reflection.
12 Or “his law.”
13 The Hebrew perfect verbal form with vav (ו) consecutive here carries the same characteristic force as the imperfect in the preceding verse. According to the psalmist, the one who studies and obeys God’s commands typically prospers.
14 Heb “channels of water.”
15 Heb “which.”
16 The Hebrew imperfect verbal forms in v. 3 draw attention to the typical nature of the actions/states they describe.
17 Heb “in its season.”
18 Or “fade”; “wither.” The author compares the godly individual to a tree that has a rich water supply (planted by flowing streams), develops a strong root system, and is filled with leaves and fruit. The simile suggests that the godly have a continual source of life which in turn produces stability and uninterrupted prosperity.
19 Heb “and all which he does prospers”; or “and all which he does he causes to prosper.” (The simile of the tree does not extend to this line.) It is not certain if the Hiphil verbal form (יַצְלִיחַ, yatsliakh) is intransitive-exhibitive (“prospers”) or causative (“causes to prosper”) here. If the verb is intransitive, then כֹּל (kol, “all, everything”) is the subject. If the verb is causative, then the godly individual or the Lord himself is the subject and כֹּל is the object. The wording is reminiscent of Josh 1:8, where the Lord tells Joshua: “This law scroll must not leave your lips! You must memorize it day and night so you can carefully obey all that is written in it. Then you will prosper (literally, “cause your way to prosper”) and be successful.”

In other versions

ESVEnglish Standard Version

but his delight is in the law of the Lord,

and on his law he meditates day and night.

He is like a tree

planted by streams of water

that yields its fruit in its season,

and its leaf does not wither.

In all that he does, he prospers.

NIVNew International Version (2011)

but whose delight is in the law of the Lord,

and who meditates on his law day and night.

That person is like a tree planted by streams of water,

which yields its fruit in season

and whose leaf does not wither—

whatever they do prospers.

CSBChristian Standard Bible

Instead, his delight is in the Lord’s instruction,

and he meditates on it day and night.

He is like a tree planted beside flowing streams

that bears its fruit in its season,

and its leaf does not wither.

Whatever he does prospers.

NLTNew Living Translation

But they delight in the law of the Lord,

meditating on it day and night.

They are like trees planted along the riverbank,

bearing fruit each season.

Their leaves never wither,

and they prosper in all they do.

LEBThe Lexham English Bible

Instead, in the law of Yahweh is his delight,

and on his law he meditates day and night.

And so, he is like a tree planted by streams of water

that gives its fruit in its season;

its leaf also does not wither.

Therefore all that he does prospers.

KJV 1900King James Version

But his delight is in the law of the Lord;

And in his law doth he meditate day and night.

And he shall be like a tree planted by the rivers of water,

That bringeth forth his fruit in his season;

His leaf also shall not wither;

And whatsoever he doeth shall prosper.

Public Domain