[Acts 26:14]:

"And when we had all fallen to the ground, I heard a voice saying to me in the Hebrew dialect, 'Saul, Saul, why are you persecuting Me? It is hard for you to kick against the goads.' "

"goads" = "kentro"

[THEOLOGICAL DICTIONARY OF THE NEW TESTAMENT, edited by Gerhard Kittel and Gerhard Friedrich, translated and abbridged in one volume by Geoffrey W. Bromiley, William B. Eerdmans Publishing Co, Grand Rapids, Mich., 1992]:

"kentron [goad, sting]

A. Outside the NT. With the basic sense of 'something that pierces,' this word is used 1. for animal claws, 2. for such human instruments as spurs, goads, scourges, or nails, 3. figuratively for torments or incitements, 4. for authority (cf. the common expression 'to kick against the goads'), and 5. mathematically for the point of a compass or the center of a circle. The LXX [Septuagint = Greek translation of the O.T.] uses the term for goad (e.g., Prov. 26:3). Philo compares God to a charioterer with rein and whip, but he also uses the term for center (the earth as the center of the cosmos). Josephus refers to the kentron of passion (cf. Antiquities 7.169) (Anmon for Tamrr) or attraction (cf. Jewish War 2.385).

B. In the NT.

1) In Acts 26:14, in Paul's conversion story, Christ tells Paul that it hurts him to kick against the goads. Although the idea of the goad for oxen is commmon in the Jewish world, Paul (or Luke [author of 'Acts']) seems to be adopting the Greek proverb here; this is most suitable in an address to the Hellenist Agrippa. It is hardly possible to prove a direct quotation (by Luke) from Euripides, who has the saying (with the plural goads) in a similar situation. In any case, the proverb (also in the plural) is a stock quotation by the first century A.D.

2) In 1 Cor 15:55ff, Paul quotes Isa 25:8 and Hos 13:14, and then adds that the kentron of death is sin. The idea here is not so much that death is a tyrant with a goad, or a soldier with a lance or arrow, or a beast with a poison tip, but rather that it is like an insect with its sting. When sin, on which its power rests, is vanquished by Christ, the sting is withdrawn and death becomes impotent.

3) In Rev. 9:10 the locust-scorpions that arise from the abyss when the fifth trumpet sounds have poisonous stings in their tails with which they torment those who do not have God's seal."

Stanley D. Toussaint states, (The Bible Knowledge Commentary, New Testament edition, Editors John F. Walvoord and Roy B. Zuck, Victor Books, USA, 1988, p. 424):

"Some believe that the statement, "It is hard for you to kick against the goads," means Paul had guilt feelings and was violating his conscience in persecuting believers in Christ. However, Paul wrote later that in spite of his blaspheming, violence, and persecution of the church he was shown mercy because he was acting in ignorance and unbelief (I Tim 1:13). Kicking the goads evidently referred to the futility of his persecuting the church."