One aspect that Pope Francis emphasises about the Synod on Synodality is 'rigidity'. At the beginning and end of the three-year-long Synod, he sternly admonishes the People of God not to be rigid. Before the Synod began, in his address to the faithful of the Diocese of Rome, he said: "Rigidity is another perversion, a sin against God's patience, a sin against God's sovereignty". (Vatican, 2021). Similarly, in the final greeting, he asked the People of God to receive the final document of the Synod on Synodality with an attitude expressed in the poetic and prayerful words of Madeleine Delbrêl: "Above all, do not be rigid." (Vatican, 2024). What does the Synod mean by the term 'rigidity' and why is the Pope so specific about this instruction to the people of God and especially to the clergy and religious? Does 'not to be rigid' mean 'to let go' or 'to let loose'? This paper attempts to reflect on what 'rigidity' is, why and how it must be avoided in a synodal way of life, and sees a remedy for this sin of rigidity in the 'unselfing act of the Holy Spirit'. After briefly analysing what the Synod means by the term 'rigidity' in the light of its final document (For a Synodal Church: Communion, Participation, Mission), I will propose the 'unselfing activity of the Holy Spirit', based on the theology of Hans Urs von Balthasar, as both a gift and a model to be valued, cultivated and followed by the People of God to avoid the sin of rigidity in building up the Synodal Church and participating in its mission.