The answer is: Psalm 117

Psalms 117:1-2 - This psalm is remarkable not only for its brevity but also for its universal call to praise. It emphasizes God’s steadfast love and faithfulness, a theme echoed throughout the Bible. Interestingly, it's the middle chapter of the entire Bible, bridging both Testaments in its declaration of worship.

Psalm 117, with its two concise verses, packs a powerful punch! In a collection that often waxes poetic on the high mountains of human experience, this shortest psalm manages to capture the essence of divine praise simply and effectively. It bursts into the airwaves of both individual and national identity, calling "all you nations" and "all you peoples" to unite in worship. It’s like a divine open mic night!

What’s really fascinating is how Psalm 117 plays a role as a centerpoint in the entire Biblical narrative. It’s like the eye of a spiritual hurricane where the good news of God's faithfulness to Israel gives way to a universal message for humanity. This signals to many across both Testaments that inclusion and grace are foundational notes in the symphony of faith.

In addition to connecting the two halves of the Bible, Psalm 117 emphasizes God's love and loyalty through repetition, resonating with themes we find in multiple mystical and prophetic books. It beckons readers to see reflections of divine persistence, echoing sentiments from Isaiah about God’s plan for all people, and even hints at the early Christian message which famously elongated this inclusivity.

So, whether you're singing it from a mountain top or under the stars, remember—you've entered a timeless invitation to recognize that divine harmony isn't bound by borders, but genuinely crosses all lines!