Here are more concrete answers: The Holy Scriptures state that the Spirit
proceeds from the Father. Our Lord Jesus Christ, on the night before
He suffered, said to His apostles (John 15:26 RSV):
+ But when the Counsellor comes,
+ whom I shall send to you from the Father,
+ even the Spirit of truth,
+ who proceeds from the Father,
+ he will bear witness to me.
The Filioque undermines the very foundations of the doctrine of the Holy Trinity,
in that it denies the nature of the Father, Whose nature it is to be the sole source from which all else is derived. Although all Three
Persons of the Trinity are co-eternal and co-equal, nevertheless the
Son is derived of the Father, and not the Father of the Son. When we
call the First Person of the Trinity the Father, we are affirming
that He imparts life and existence to others, for this is what it
means to be a father. It is NOT what it means to be a Son, and
therefore it is wrong to suppose that the being of the Spirit is
derived from the Son as well as from the Father.
John 15:26:
But when the Counselor comes, whom I shall send to you from the Father, even the Spirit of truth, who proceeds from the Father, he will bear witness to me."
John 16:7:
Nevertheless I tell you the truth: it is to your advantage that I go away, for if I do not go away, the Counselor will not come to you; but if I go, I will send him to you.
John 20:22:
And when he had said this, he breathed on them, and said to them, "Receive the Holy Spirit."
John 16:15:
All things whatsoever the Father hath are mine. Therefore I said that he shall receive of me and show it to you.