“Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, who has made us sufficient to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life.” [2 Cor 3:5-6 ESV]
Assume that we were able to construct our own spirituality: what guarantee do we have that we've got it right? How can our own spirituality be right if our own compositions are so different?
The COEXIST bumper sticker is a lie because the gods represented there disagree with one other and the followers are not listening! Tolerate all you want: the god of my personal understanding (whoever he or she is) will always be greater than yours!
The true and living God gave us a new covenant in Christ Jesus. "For this is My blood of the new covenant, which is shed for many for the remission [forgiveness] of sins.” [Mat 26:28]. There is true spirituality!