وَأَلقَى فِى ٱلأَرضِ رَوَسِىَ أَن تَمِيدَ بِمۡ وَأَنہَـرًا وَسُبُلاً لَّعَلَّڪُم تَہتَدُونَ (
And He hath cast into the earth firm hills that it quake not with you, and streams and roads that ye may find a way. (15)
TAFSEER FROM DR. FARHAT HASHMI
Allah Subhanawataala made Mountains to balance the earth, which is uneven and has depths and recesses as well as higher parts.
The mountains give it stability and prevent the earth from shaking and rocking like a stretched piece of cloth with no anchor e.g. with earthquakes
The rivers and streams on earth are a naimah (blessing) their intricate web covering the earth like arteries cover and nourish the body. Along with the natural paths all over the world.
Human beings have always used these natural paths to find ones destination and to thus in gratitude find and recognize God as our Creator.
Elsewhere in the Quran Allah Subhanawataala says regarding His creation of mountains:
Surah Naba 78:5-7
Verily, verily they shall soon (come to) know! (5) Have We not made the earth as a wide expanse, (6) And the mountains as pegs? (7)
Surah Naziaat: 79:32
And the mountains hath He firmly fixed― (32)