The First Psalm

Psalm 1 King James Version (KJV)

1 Blessed is the man that walketh not in the counsel of the ungodly, nor standeth in the way of sinners, nor sitteth in the seat of the scornful.

2 But his delight is in the law of the Lord; and in his law doth he meditate day and night.

3 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.

4 The ungodly are not so: but are like the chaff which the wind driveth away.

5 Therefore the ungodly shall not stand in the judgment, nor sinners in the congregation of the righteous.

6 For the Lord knoweth the way of the righteous: but the way of the ungodly shall perish.

The major literary device is this psalm is juxtaposition or contrast. It seeks to portray its message of righteousness by contrasting the blessings of obedience to the curses brought on by the flouting of "the Law of the Lord". 

A simile is used in the third verse to highlight the exponential growth and prosperity which is garnered by adherence to divine will. Waters signify blessings and a constant source of nutrients for the tree similar to how the Word of God is meant to be like one's daily bread. Also, in the most apropos time and season in accordance with divine will and guidance, the believer will produce the necessary physical and spiritual fruits. The extended simile even has a promise of longevity when it is contended that their leaves will not whither. In other words, their contributions and blessings will not be unsteady and fickle but since they are delivered in the appropriate season based on God's will, it will stand the test of time, even unto eternity. 

A tree takes a long time to grow and mature. Some trees can take seven to ten years while some take longer. Some trees have survived for centuries. The tree smile is one which connotes the virtue of patience with one'self and with the Divine. Spiritual growth and sanctification is the work of a lifetime and believers must be patient with themselves while trusting the process of the journey which God takes them own. Salvation is personal and each while have his or her own path/process. 

The "chaff" simile used in verse four of the chapter is attributed to the "ungodly". The Merriman-Webster dictionary refers to chaff as:

1: the seed coverings and other debris separated from the seed in threshing grain

2: something comparatively worthlessa few kernels of wisdom amid much discursive chaff— Steven Raichlen

3: the scales borne on the receptacle among the florets in the heads of many composite plants

This simile mightily captures the transient nature of the works and blessings accumulated by the enemies of God. It also connotes how insignificant there lives can be since they have barred themselves from a promise of eternity. It is also significant to note that the image of the chaff being blown haphazardly on the wind has some synergy with the Ephesians 4:14 which states: 

That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive;

Therefore, the verse is warning to all believers, non-believers, everyone for we are all loved by God. The closing verse can be seen as a soul-racking ultimatum from a Supreme Being or the balm-like plea of a worried parent.