When John the Baptist appeared as Christ’s forerunner, God’s chosen people had lived under the law of Moses for fifteen hundred years but had not kept it. Hence John’s call to repentance and baptism for the remission of sins (Mark 1:4).
John was in earnest, too, for when the thoughtless multitude came to him to be baptized, he sent them back, saying: “Bring forth fruits worthy of repentance” (Luke 3:7,8).
Their lives were to be changed and they were to show it. When the people asked: “What shall we do, then?” he told them to live for others rather than for self (Luke 3:10,11). When the tax collectors asked: “What shall we do?” he demanded that they stop cheating the tax payers and live honestly (Vers. 12,13). When the soldiers asked: “What shall we do?” he told them to forbear violence, false accusation and bribery (Ver. 14).
Clearly, righteousness was demanded under John’s message. His hearers were to repent, be baptized, and bring forth the fruits of true repentance. When our Lord appeared, He proclaimed the same message as John (Matt. 3:1,2; 4:17). A lawyer asked: “What shall I do to inherit eternal life?” and He replied: “What is written in the law?” When the lawyer recited the basic commands of the Law, our Lord answered: “This do and thou shalt live” (Luke 10:25-28). God was still demanding righteousness. They were all under the Law (Gal. 4:4,5; Matt. 23:1,2; etc.).
Some suppose this was all changed after Calvary by the so-called “great commission.” This is not so. When, at Pentecost, Peter’s hearers were convicted of their sins and asked “What shall we do?” Peter commanded them to “repent and be baptized… for the remission of sins” just as John had done (Mark 1:4; cf. Acts 2:38). He did not tell them that Christ had died for their sins.
Paul was the first to say: “But now the righteousness of God without the law is manifested… [We] declare His righteousness for the remission of sins” (Rom. 3:21-26). When the Gentile jailor fell on his knees and asked: “What must I do to be saved?” Paul replied: “Believe on the Lord Jesus Christ and thou shalt be saved” (Acts 16:30,31). This is God’s message for sinners today, for “we have redemption through [Christ's] blood, the forgiveness of sins according to the riches of His grace” (Eph. 1:7).
C.R. Stam, Two Minutes With the Bible