Paul reminds them their pagan past implying their lack of experience with true "inspired speech".
Since "inspired utterance" itself is not evidence of being "led by the Spirit"; Paul gives them the criterion to test the spirits (like 1Jn 4:1-3) and to judge the authentic from the inauthentic. The ultimate criterion of the Spirit's activity is the exaltation of Jesus as Lord. "Jesus is Lord" is not just verbal confession but true and absolute allegiance to Jesus as one's master.
Trinity (Spirit/Lord/God) itself is a diversity within unity. In v.4-11, the repetition of "same" stresses unity while the repetition of "each one" stresses diversity.
Objective of spiritual gifts: "for the common good" or "to build the body of Christ" (Eph 4:12).
Paul has 6 other lists in this letter (12:28,29-30; 13:1-3,8; 14:6,26), each of which is also ad hoc (simply spun off at the moment for the purpose of the argument); no two of which are exactly alike either in language, number, or character. Thus the lists are neither carefully worked out nor exhaustive; they are merely representative of the diversity of the Spirit's manifestations. The emphasis of this list is on the supernatural manifestation.
(a) message of wisdom: not the wisdom of the Corinthians (ch.1-2) but a message that Christ crucified is God's true wisdom
(b) message of knowledge: a spiritual utterance of some revelatory kind
(c) faith: special gift of supernatural faith that can "move mountains" (mentioned again in 13:2)
(d) gifts of healing: the plural probably suggests not a permanent "gift" but that each occurrence is a "gift" in its own right.
(e) miraculous powers (or workings of miracles): all other kinds of supernatural activities beyond the healing of the sick, again the plural probably suggests not a permanent "gift"
(f) prophecy: In Old Testament, the prophet was a person who spoke to God's people under the inspiration of the Spirit. The job is to "foretell" or to "forthtell"; thus prediction is only one element. Evidence in chapter 14 indicates that it consisted of spontaneous, Spirit-inspired, messages, orally delivered in gathered assembly, intended for the edification or encouragement of the people (that is, not the delivery of a prepared sermon).
(g) distinguishing between spirits: probably not testing the spirits (1Jn 4:1) but related to 14:29 where Paul calls for testing or discerning of prophetic utterances (also 1Th 5:20-21)
(h) tongues: Evidence from Ac 2:5-11 and the need for interpretation (14:27-28) probably point to an actual language; yet 14:10-11,14 imply that it is not a known earthly language. Because of the contradictory sayings in ch.14, a suggested solution is that there are two different manifestations of tongues, one of ecstatic languages of praise and prayer (not a known language), another actual languages but unknown to the speaker. In assemblies, tongues can only be used when they are interpreted by the same person or someone else.
(i) interpretation of tongues: because of the unintelligibility, to articulate for the benefit of the community what the tongues-speaker has said; 14:5,13,27-28 indicates that it may be given either to the tongues-speaker or to another.
Paul emphasizes the sovereignty of the Holy Spirit in distributing the gifts.