The gemara[1] says: “Whoever sets a place for his prayers, the God of Avraham will help him, and when he dies they will say of him: ‘what a humble, righteous man, a student of our father, Avraham.’” Some explain that a set place makes it easier for one to concentrate.[2] Others say it is a sign of humility and trust in HaShem, which Avraham demonstrated by davening in the same place. Bilam, on the other hand, tried his luck in several places.[3] Others take more mystical approaches.
The commentators explain that the main intent of this halachic preference is to consistently daven in one shul. The particular place within the shul is a secondary component.
Practically, what should one do if he finds his set seat occupied? The consensus of the poskim, which follows the Magen Avraham’s[4] opinion, is that a makom kavua extends four amot[5] around one’s place.[6] If one can find a free seat within that radius, there is no reason to ask someone to move. Furthermore, one may move from his makom kavua for an important reason.[7] Avoiding making others feel uncomfortable is certainly reason enough. (“Students of Avraham” should make hachnasat orchim[8] a priority). Additionally, some explanations imply that there is a concern only if one moves of his own accord.
If someone is not very careful about always davening in one shul, coming on time, keeping quiet, and other central laws of tefilla, it would be strange to choose makom kavua as his area of piety at the expense of others. Too many Jews have been “turned off” after weeks in a shul, concluding: “The only words anyone ever said to me were, ‘You’re in my seat.’” Although we must avoid pointing fingers at others for the hurt feelings of some newcomers, we must also deal with the problem.
A legitimate claim one can employ if he wants to remove someone from his seat is ownership of the seat. However, we would suggest that one not make such a claim against a first time, unintentional user of his seat, especially when the owner comes before HaShem asking Him to overlook his imperfections.[9] If one is himself a guest or newcomer, he should avoid sitting in another’s seat. He should realize that many people find moving their seats disorienting, and they should be allowed to maximize their tefilla. In general, one should strive to see things from his counterpart’s perspective.
It is wise for a shul to have a clear policy regarding members’ rights and limitations thereon (e.g., you can ask someone to move until Barchu) and to have gabba’im greet newcomers and direct them to a safe haven.