For ye have heard of my conversation in time past in the Jews' religion, how that beyond measure I persecuted the church of God, and wasted it:
Note 3 at Ga 1:13: The Galatians had heard about Paul's former conduct and manner of life in Judaism. The Scriptures do not make it clear how they knew this. They may have heard by word of mouth or from Paul himself.
The phrase "in time past" refers to his former life before meeting Jesus Christ. Paul's religious zeal is referred to in Php 3:5-6 where he described himself as "an Hebrew of the Hebrews; as...touching the righteousness which is in the law, blameless"; i.e., he "tried to obey every Jewish rule and regulation right down to the very last point" (Php 3:6, The Living Bible). He was in a religious system, like all of the world's religious systems, that tried to achieve righteousness before God by human effort. When confronted by the claims of Jesus Christ and the real truth proclaimed in the Law, he realized he was the chief of sinners (1Ti 1:15). He learned that by the works of Law, no person could ever be justified (Ga 2:16) and that the Gospel was a Gospel of grace (Ac 15:11 and 20:24).
Notice that his religious zeal led to the persecuting of those preaching the Gospel of grace. Paul went on to speak more about this later in his epistle through the illustration of Ishmael and Isaac (Ga 4:21-31). False religion has always persecuted true religion, and it will continue to be this way until the end of the age. Law and grace are two different ways of approaching God with opposite results (see Ro 9:30-10:10). They are not two different ways of receiving the same thing.
In the Greek, the imperfect tense is used of both "persecuted" and "wasted." This implies the persecution that Saul brought against the church was consistent, in excess, without mercy, and continued for some time. The imperfect tense of the verb for "wasted" indicates an attempt, as well as an action, to "destroy" the church that continued for a period of time (UBS Handbook, p. 19).