I love how so many of the psalms are encouraging, comforting, convicting and instructive, all at the same time. God is like that.
Psalm 4
For the director of music. With stringed instruments. A psalm of David.
1 Answer me when I call to you,
O my righteous God.
Give me relief from my distress;
be merciful to me and hear my prayer.
Right off the bat, I identify with David's desire for God to hear and answer. Look how he characterizes God: righteous. Merciful. Has the power to calm and comfort.
2 How long, O men, will you turn my glory into shame?
How long will you love delusions and seek false gods?
Selah
I have to think this isn't David. Literally, 'sons of men' are addressed here. I take it as the Lord asking these questions. How long will we allow deception to penetrate our hearts? How long before we will cast aside lies and delusion, and follow the Lord's commands to love, obey, and serve?
That challenges my heart.
3 Know that the LORD has set apart the godly for himself;
the LORD will hear when I call to him.
David again. I love his confidence that God WILL HEAR and, by implication, protect and deliver.
4 In your anger do not sin;
when you are on your beds,
search your hearts and be silent.
Selah
5 Offer right sacrifices
and trust in the LORD.
Verse four is an important verse in my eyes, because it's one of the places in Scripture where we can begin to understand how God views anger. Many people think that anger in itself is wrong--it's not. Jesus was quite angry as he drove the moneychangers from the Temple (unless you think he 'mildly' mentioned to them that they'd made His Father's house a den of robbers [Matt 21]!).
Without going into a word study on anger right now (because the Bible does have a good bit to say about it), we can know that the bottom line for those who love God is this: "In your anger, do not sin." Anger is like a fire. It can be extremely dangerous, or it can be harnessed and controlled.
6 Many are asking, "Who can show us any good?"
Let the light of your face shine upon us, O LORD.
7 You have filled my heart with greater joy
than when their grain and new wine abound.
I see here a contrast between the godly and the wicked. Those who do not have the Lord may become despondent and jaded, but the lover of God looks to Him for sustenance and joy. In Him is no darkness at all (1 John 1:5).
It also calls to mind Jesus' assertion that He is the bread of life (John 6:35). Others' god may be their stomachs, but ours ensures we will never hunger and thirst again.
Phil 3:18-20
For I have told you often before, and I say it again with tears in my eyes, that there are many whose conduct shows they are really enemies of the cross of Christ. Their future is eternal destruction. Their god is their appetite, they brag about shameful things, and all they think about is this life here on earth. But we are citizens of heaven, where the Lord Jesus Christ lives. And we are eagerly waiting for him to return as our Savior.
And finally,
8 I will lie down and sleep in peace,
for you alone, O LORD,
make me dwell in safety.
I love to think about how much David trusted God. I think about the nights David faced, watching as dusk fell, knowing that Saul was pursuing him to take his life. David chose to remember that God is sovereign. He trusted the God he knew.