On account of my love they have been opposed to me [1] The Psalmist had already solemnly declared, that his adversaries, unprovoked by any injury inflicted upon them by him, and without any just cause, became, through mere diabolical rage, his most implacable foes. Here he confirms the truth of that declaration by saying, that he had been their friend. For there is far more merit in showing kindness to an enemy than simply abstaining from doing that which is evil. And from this we may perceive, that the influence of Satan must be awfully powerful when he takes the hearts of men captive at his will. For nothing can be more unnatural than to hate and cruelly persecute those who love us. To love he also adds deeds of kindness, meaning, that it was his aim to secure their good will by outward acts of beneficence.

Footnotes

1 - "This expression," says Hengstenberg, "finds its full truth in Christ. Christ's love to man was daily manifested by his miraculous healing all the infirmities of the body, which was returned by man's hatred of Him, as displayed in his general conduct."

For my love - As a recompence for my love; or, this is the return which I get for all the expressions of my love to them. The enemies referred to were those whom he had treated kindly; to whom he had done good. This is not uncommon in the world. It was illustrated in an eminent degree in the life of the Saviour.
But I give myself unto prayer - literally, "I - prayer;" that is, I am all prayer; I continually pray. This may mean, either, that he bore these trials with a meek spirit, and did not allow these things to disturb his devotions; or, more probably, that he prayed constantly "for them;" he desired their good, and sought it from above.

For my love they are my adversaries - In their behalf I have performed many acts of kindness, and they are my adversaries notwithstanding; this shows principles the most vicious, and hearts the most corrupt. Many of the fathers and commentators have understood the principal part of the things spoken here as referring to our Lord, and the treatment he received from the Jews; and whatever the original intention was, they may safely be applied to this case, as the Psalm 109:2, Psalm 109:3, Psalm 109:4, and Psalm 109:5 are as highly illustrative of the conduct of the Jewish rulers towards our Lord as the following verses are of the conduct of Judas; but allowing these passages to be prophetic, it is the Jewish state rather than an individual, against which these awful denunciations are made, as it seems to be represented here under the person and character of an extremely hardened and wicked man; unless we consider the curses to be those of David's enemies. See the note on Psalm 109:20 (note).
But I give myself unto prayer - ואני תפלה vaani thephillah; "And I prayer." The Chaldee: ואנא אצלי vaana atsalley, "but I pray." This gives a good sense, which is followed by the Vulgate, Septuagint, Ethiopic, Arabic, and Anglo-Saxon. The Syriac, "I will pray for them." This, not so correctly; as dreadful imprecations, not prayers, follow. But probably the whole ought to be interpreted according to the mode laid down, Psalm 109:20. The translation and paraphrase in the old Psalter are very simple: -
Trans. For that thyng that thai sulde hafe lufed me, thai bakbited me; bot I prayed.
Par - That is, that sulde haf lufed me for I was godson, and thai bakbited me sayande, in Belzebub he castes oute fendes; bot I prayed for thaim.

For my love they are my adversaries: (b) but I [give myself unto] prayer.
(b) To declare that I had no other refuge, but you, in whom my conscience was at rest.

For my love they are my adversaries,.... For the love that Christ showed to the Jews; to their bodies, in going about and healing all manner of diseases among them; to their souls, in preaching, the Gospel to them in each of their cities; and for the love he showed to mankind in coming into the world to save them, which should have commanded love again; but instead of this they became his implacable adversaries: they acted the part of Satan; they were as so many Satans to him, as the word signifies.
But I give myself unto prayer; or "I am a man of prayer" (y); as Aben Ezra and Kimchi supply it; so he was in the days of his flesh, Hebrews 5:7, he was constant at it, and fervent in it; sometimes a whole night together at it: his usual method was, when at Jerusalem, to teach in the temple in the daytime, and at night to go to the mount of Olives, and there abide and pray, Luke 6:12. This was the armour he alone made use of against his enemies, when they fought against him, and acted the part of an adversary to him; he betook himself to nothing else but prayer; he did not return railing for railing, but committed himself in prayer to God, who judgeth righteously, 1-Peter 2:23, yea, he prayed for those his adversaries: and so Aben Ezra and Kimchi interpret it, that he was a man of prayer for them, and prayed for them; as it is certain Christ did, when he was encompassed by his enemies, and they were venting all their spite and malice against him, Luke 23:34.
(y) "et ego vir orationis", Pagninus, Gejerus.

They return evil for good (compare Psalm 27:12; Proverbs 17:13).
I give myself unto prayer--or literally, "I (am) prayer," or, "as for me, prayer," that is, it is my resource for comfort in distress.

Adversaries - They requite my love with enmity, as it is explained Psalm 109:5.