God is infinite. Limitless. Boundless.
This means that our best efforts to understand God will always fall short. It also means that it is always possible for us to grow in understanding. We cannot reach the limits of knowing God. Our human minds are not up to the job. All the world could be filled with books and still not have exhausted the mystery of God, or the love of God, or the mercy of God.
In the Bible, the Book of Psalms is a case in point. As a collection of poetry, the Book of Psalms has beauty and depth and richness. And even though it contains so many songs, it keeps sending out the call to "sing a new song". In a way, the Book of Psalms will never be complete. Technically, sure, it has so many psalms and that's all. In that sense it has been complete down through the ages. But nearly every day someone in the world writes a new song to praise God. They are living out the Bible just as surely as the one who feeds the hungry and visits his neighbor. The Bible is a living book because our God is a living God. God's mercies are new every morning; it follows that there is always something more.
Our hymnals have one thing right: the Psalms and the hymns we still sing are, in a very real sense, part of the same work.