The Latin term "filioque" was added to the original Niceno-Constantinopolitan Creed (commonly known as the Nicene Creed), which has lead to great controversy between the Eastern and Western churches. The term describes the Holy Spirit as proceeding from both the Father and the Son, and not from the Father only. Whether or not the term is included, some say that it implies a serious underestimation of the Father's role in the Trinity, while others say that it implies a serious underestimation of the Son's role in the Trinity. Both these groups are in the wrong. Whether it is included or not does not underestimate either the Father's or the Son's role in the Trinity. However, by having the term included actually makes the Creed more biblical. Observe:
"I will ask the Father, and He will give you another Comforter, that He may be with you forever;" John 14:16
"But the Comforter, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all that I said to you." John 14:26
"When the Comforter comes, whom I will send to you from the Father, that is the Spirit of truth who proceeds from the Father, He will testify about Me," John 15:26
"But I tell you the truth, it is to your advantage that I go away; for if I do not go away, the Comforter will not come to you; but if I go, I will send Him to you." John 16:7
According to the first two verses, the Comforter—the Holy Spirit—proceeds from the Father. According to the last two verses, the Holy Spirit proceeds from the Son. In the last two verses, Who sends the Holy Spirit? Jesus. All three Persons of the Trinity were involved in creation, the birth of Jesus, the resurrection of Jesus, salvation, etc., etc., etc. So it is no surprise that the Holy Spirit would be sent by both the Father and the Son. This fact should end the controversy between the Eastern and Western churches.
The Eastern Orthodox church, the Oriental Orthodox churches, and the church in the east are in error for rejecting the addition of this term, seeing as how it is derived directly from Scripture.