But may all who seek you
     rejoice and be glad in you;
may those who love your salvation
    say continually, “Great is the Lord!"

David's prayer in Psalm 40:16 can absolutely change your life. At first glance it may not stand out. Perhaps, like me, when you've read it before you glossed over the parallelism that makes this verse so special.

Now parallelism is a pretty simple rhetorical device. It is used in poetry of all kinds to connect two different phrases within a single line, always extending (in some way) the thought in the first phrase.¹ Verse 16 below is one line with two phrases that are signified by A and B:

The particular type of parallelism is called “synonymous parallelism.” It basically is used by a poet to state the same idea in two different ways. It's not something we should breeze by. Instead read it and reread it. The point is for it to resound in the reader's mind.

So what is David saying in Psalm 40:16? David prays that all who seek God would rejoice and be glad in him. This is the first phrase, that the end of seeking God be joy in God. Now notice how this idea is repeated (and extended) in the second phrase: May all who love your salvation say continually, “Great is the LORD!”

As the phrases correspond, to seek God is parallel to loving his salvation, and to rejoice in God is parallel to praising him. The aim, then, of seeking God and loving his salvation is to rejoice in him and glorify him.

Seeking As Loving

To seek God in this passage means to pursue him. A seeker, according to this verse, is not someone who is merely interested in religious topics. Rather than having reservations about God, the seeker is one who is in passionate pursuit to know him. The seeker is locked in, and keeps yearning for more. Specifically, this work of seeking — of pursuing God — is to love his ways. If you will seek God like David prays, you will cherish the salvation only God can give. If you will know him, you will know him only through his Son (Matthew 11:27).

So there's no such thing as seeking God outside the blood and righteousness of Jesus. To seek him is to revel in and cling to all that he is for us in the gospel. To love his salvation is to be bewildered by what he's done to bring us to himself.

Rejoicing As Glorifying

You can't faithfully seek God, or love his salvation, with any legitimate aim other than to rejoice in him. That is the goal. There are really no other options. Seeking isn't spinning our wheels. There is an end in sight, a real end — when we see Jesus as he is and become perfectly conformed to his image (1 John 3:2), when the dwelling place of God will be with man in a new world (Revelation 21:1–3), when we live and reign with Jesus forever, his name written on our foreheads and his light making the night no more (Revelation 22:3–5). This will be a happy scene. We will rejoice in God. We will be glad in God. And he will be glorified. In fact, they are one in the same.

As the phrases show, rejoicing in God means to praise his name. Joy equals doxology. This kind of gladness in Psalm 40:16 sounds a certain way, like a chorus of rescued voices. It speaks a certain language, like a song from all the nations. And it says a certain thing: “To him who sits on the throne and to the Lamb be blessing and honor and glory and might forever and ever!”

¹ Tremper Longman, How to Read the Psalms, (Kindle Locations 1455-1456).