The journey of the Israelites through the desert was marked by a recurring cycle of disbelief. Time after time, they returned to their old behaviors and patterns of doubt [ביאור שטיינזלץ, מלבי״ם]. After demanding meat, they tested God again at the waters of Meribah, along with other instances not explicitly recorded in the Torah [רד״ק, מאירי, מצודת דוד]. They carried out these trials even though it was already clear to them that He is indeed God [אבן עזרא], and despite the constant kindness He showed them [אלשיך]. Their actions were a way of checking whether God, despite His absolute power, was truly capable of fulfilling their constantly changing needs at every moment [רד״ק, מלבי״ם].
The core of their failure lay in how they attempted to define God. The primary approach among commentators is that the Israelites placed mental boundaries around Him, believing He could accomplish certain things but not others. By doing this, they attempted to measure His power, effectively denying His absolute capability and rejecting the belief that He could alter the laws of nature [רד״ק, אבן עזרא, מלבי״ם, מאירי]. Another perspective suggests they constantly demanded signs, turning God into a target for their trials by repeatedly asking for wonders to prove He was truly among them [רש״י, מצודת ציון, מצודת דוד, ביאור שטיינזלץ]. A further unique view explains their behavior as a form of physical pointing; just as they pointed at the Red Sea and declared His presence, they metaphorically marked and pointed at Him again in their demands [אלשיך].
This diminishing behavior stood in direct contradiction to His identity as the Holy One of Israel. God had already been sanctified before their eyes through countless signs and wonders [רד״ק]. He is holy and exalted far beyond their narrow, limiting thoughts [אבן עזרא]. Yet, by continuing to subject Him to their tests, they not only failed to recognize His true greatness but also caused Him deep sorrow [ביאור שטיינזלץ].