I have been trying to understand the Cath/Orthodox schism, and one issue was the insertion of the Spirit proceeds from the Father and Son, not just the Father. The most illuminating thing I came across was at the end of Catechism CCC 248 ... '**provided it does not become rigid'. **It alerted me to the fact that with things of God, we can't expect to be able to pin Him down with satisfying summations. He is God; He doesn't have to satisfy our desire to dominate Him. **'At the outset the Eastern tradition expresses the Father's character as first origin of the Spirit. By confessing the Spirit as he "who proceeds from the Father", it affirms that he *comes from* the Father *through* the Son. *[Jn 15:26; cf. AG 2.]* The Western tradition expresses first the consubstantial communion between Father and Son, by saying that the Spirit proceeds from the Father and the Son *(filioque)*. It says this, "legitimately and with good reason", *[Council of Florence (1439): DS 1302.]* for the eternal order of the divine persons in their consubstantial communion implies that the Father, as "the principle without principle", *[Council of Florence (1442): DS 1331.]* is the first origin of the Spirit, but also that as Father of the only Son, he is, with the Son, the single principle from which the Holy Spirit proceeds. *[Cf. Council of Lyons II(1274): DS 850.]* This legitimate complementarity, provided it does not become rigid, does not affect the identity of faith in the reality of the same mystery confessed.' **
