The Psalms are poems. In any language, poetry is different from prose. Much of the poetry we're used to uses rhyme and rhythm. Hebrew poetry didn't do it this way. One key element of their poetry had to do with repetition. So, a line of Hebrew poetry would repeat and develop the idea that was said in the previous line. And that's what's going on in our verses.
For the word of the Lord is upright,and all his work is done in faithfulness.By the word of the Lord the heavens were made,and by the breath of his mouth all their host. Psalm 33.4,6
We encounter here a common biblical theme: God's work is associated with His word. Or to say that differently, God does things by speaking. An obvious example would be found in Genesis 1. 'And God said … And it was so.' God created everything we see (and more) simply by speaking some words. Here, we have one example of God's power.
That power is still expressed today. Every time God's words, the Bible, are read, sung, preached or taught, God is doing something. He is advancing His Gospel either by doing good to His saints or by bringing destruction on His enemies. So God says:
For as the rain and the snow come down from heaven and do not return there but water the earth, making it bring forth and sprout, giving seed to the sower and bread to the eater, so shall my word be that goes out from my mouth; it shall not return to me empty, but it shall accomplish that which I purpose, and shall succeed in the thing for which I sent it. (Isaiah 55.10-11)