The Tribe of Issachar held a distinct role in the establishment of King David's kingdom. While other tribes contributed primarily through military strength, the men of Issachar brought wisdom, vision, and strategic leadership.
The primary approach among commentators is that these men possessed a broad understanding of the world. They were able to analyze current events, anticipate future outcomes, and offer the right advice for any situation. Specifically, they guided David on how to solidify his rule against the competing house of Saul, advising him on both civil administration and military strategy [רש״י, רלב״ג, מצודת דוד, ביאור שטיינזלץ].
Alongside this strategic role, the Sages explain that their unique insight referred to a mastery over the calendar and time itself. They were experts in astronomy, calculating seasons, tracking constellations, and determining leap years and new moons [רד״ק, מלבי״ם, מצודת דוד, ביאור שטיינזלץ]. This expertise allowed them to instruct the Israelites on exactly when and how to observe the festivals. King David required these specific experts by his side, as the authority to declare leap years and set the calendar rested with the crown [רד״ק]. Another perspective suggests they served as legal advisors to the king, possessing deep knowledge of laws and judgments [רד״ק בשם ר' יונה]. However, this legal interpretation is challenged. If their primary role was to advise the king on legal matters, their guidance would have been directed specifically at the king's actions, rather than instructing the entire nation. Thus, the idea that they managed the national calendar aligns more naturally with their role [רד״ק].
Rather than sending a massive army, the tribe sent a concentrated delegation of two hundred leaders. These commanders of thousands arrived as representatives to crown David [מלבי״ם]. In later generations, this elite group was identified with the heads of the Sanhedrin, the high court [ביאור שטיינזלץ]. Even though only these two hundred men traveled to David, the rest of the tribe remained in their territory and completely submitted to their leaders' authority. They followed their instructions without question. Consequently, the arrival of these two hundred representatives was viewed as if the entire Tribe of Issachar had personally stood before David to pledge their support [רש״י, מצודת דוד].