The apostle asks that the Spirit of wisdom and revelation be given to the Ephesians. Most of the translations have “spirit” instead of “Spirit” (= the Holy Spirit). In favor of Spirit, however, are the following arguments:
(1) Paul writes “… of revelation.” We do not generally associate revelation with the purely human spirit or state of mind.
(2) As to “… of wisdom,” in Isa. 11:2 this is mentioned as the first of several gifts imparted by the Spirit of Jehovah.
(3) Such expressions as “Spirit of truth” (John 15:26) and “Spirit of adoption” (Rom. 8:15) also refer to the Holy Spirit.
(4) Ephesians abounds with references to the third Person of the Holy Trinity. Since the Comforter figured so prominently in this epistle, we may well believe that also in the present instance Paul has him in mind.
(5) It is rather characteristic of Paul that, having made mention of God the Father and of Christ the Son — and both have already been mentioned here in 1:16 — he then also refers to the Spirit. Cf. Rom. 8:15–17; II Cor. 13:14; Eph. 1:3–14; 3:14–17; 4:4–6; 5:18–21.37
(6) When the Father gives enlightened eyes, does he not do so through the Holy Spirit? See John 3:3, 5. Men cannot see the Kingdom of God, to enter it, except through the Spirit. Cf. Eph. 5:8; I John 1:7.
A question may occur, however, in this connection. It may be asked, “But how is it possible that Paul prayed that the Spirit of wisdom and revelation be given to those who already possessed that Spirit; in fact, according to verse 13, had been sealed by him?” One cannot escape this difficulty by reading “spirit” (state of mind) instead of Spirit (Holy Spirit). For even then the question would occur: “How can the apostle ask that a spirit of wisdom in the clear knowledge of him [that is, of God] be given to those who already knew him so well that they had reposed their trust in him?” (verse 13). However, this difficulty confronts us not only here in Ephesians, but throughout Paul’s epistles. To give but two examples: contrast Col. 1:4 with 3:12; I Thess. 1:3; 2:13 with 5:15. If Paul could say the one how could he say the other also?
The answer is provided by Paul himself. It amounts to this: what is already present must be strengthened. The Holy Spirit is present, to be sure, but the apostle prays that the Ephesians “may be strengthened with power through his Spirit in the inner man” (3:16). The work begun in the heart must “be carried on toward completion” (Phil. 1:6). Love and all the other graces must “abound more and more” (Phil. 1:9; cf. I Thess. 3:12; 4:10). It is clear, therefore, that Paul’s prayer here in Eph. 1:15–23, including therefore also verse 17, is entirely consistent with what he had solemnly declared in verses 3–14. In fact, the connection between verses 15 and 16, on the one hand, and 17 ff., on the other, shows that it was exactly because so many spiritual gifts had been received that the apostle takes courage to ask for even more.
Paul, then, asks that the addressed may receive a continually growing supply of wisdom and clear knowledge. Combine the two, and note that he is asking that the Ephesians be given deeper penetration into the meaning of the gospel and a clearer insight into the will of God for their lives, enabling them at all times to use the best means for the attainment of the highest goal, namely, the glory of God Triune.
Now it was the Spirit who imparted wisdom, the Spirit also who revealed the truth. For these early Christians, who so recently had emerged from pagan fear, superstition, and immorality, who were able to communicate with Paul only by letter or through a messenger, and who were living in the midst of a heathen environment, wisdom and revelation were doubly needed, and this not only in order to gain a clearer insight into the way of salvation but also to know just what was the right course to follow in any given situation. What they needed above all was clear knowledge of God, including joyful recognition of God’s way for their lives and a willingness to follow his direction.

Hendriksen, W., & Kistemaker, S. J. 1953-2001. Vol. 7: New Testament commentary : Exposition of Ephesians. Accompanying biblical text is author's translation. New Testament Commentary . Baker Book House: Grand Rapids