When John the Baptist and the Lord Jesus Christ appeared on earth, God's people had been under the law of Moses for fifteen hundred years. No wonder John and Jesus Christ looked for fruit among them.
For the grace of God has appeared, bringing salvation for all people, training us to renounce ungodliness and worldly passions, and to live self-controlled, upright, and godly lives in the present age, waiting for our blessed hope, the appearing of the glory of our great God and Savior Jesus Christ,14 who gave himself for us to redeem us from all lawlessness and to purify for himself a people for his own possession who are zealous for good works (Titus 2:11-14).
When the hypocritical religious leaders came to join John's growing audience and asked to be baptized, John called them a "brood of vipers" and told them to "bear fruit in keeping with repentance" (Matt 3:7-8). True repentance, with fruit to prove it, was the basic requirement of the earthly kingdom John proclaimed. This is evident from his declaration:
Even now the axe is laid to the root of the trees. Every tree therefore that does not bear good fruit is cut down and thrown into the fire (Matt 3:10).
Our Lord appeared, proclaiming the same message as John, and also looked for fruit among His people (Matt 7: 16-20; 21:33-43). We know, however, that John the Baptist was beheaded and Christ crucified. The fruit produced under the Law was puny indeed. Even after the resurrection of Christ, the majority of His people refused to repent and failed to produce the required fruit.
But what the Law requires, grace provides. It was at this time that God raised up the Apostle Paul, whose preaching of "the word of the cross" (1 Cor 1:18) showed that Christ had not died an untimely death, but in infinite love had come into the world to die for sinners so that they might be saved by grace, through faith alone (Eph. 2:8-9). Paul's message was called "the gospel [good news] of the grace of God" (Acts 20:24), and where the Law had failed to produce fruit, grace produced it in spades.
When Paul wrote to the Colossians that his good news was going out into all the world, he added: "it is bearing fruit and increasing—as it also does among you, since the day you heard it and understood the grace of God in truth" (Col 1:5-6 cf. Rom 6: 21-22).
In fact, grace trains us to produce good fruit.