It is the church’s purpose to bear witness to the truth of Jesus Christ in light of the Day to come. Jesus—the Judge—has called each church member up to the witness stand in their life, and we are called to testify to the truth.
So, if it’s all about our testimony of words, does our testimony of lifestyle matter?
Yes, because our lifestyle testifies.
Below is a briefly edited excerpt from the book The Gospel of Christ Crucified by John Harrigan, that explains the importance of the lifestyle of the witness.
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Those who proclaim the hope of the age to come must actually live for the age to come.
Believers are repeatedly exhorted to "walk in a manner worthy of the calling to which you have been called" (Eph. 4:1; cf. Phil. 1:27; Col. 1:10; 1 Thess. 2:12).
If we proclaim that the saints will rule the earth in the age to come, then what happens when unbelievers see us squabbling over the trivial things of this age? When we proclaim that the age to come will be full of righteousness, peace, and love, and yet we tear one another down with our words, then we "grieve the Holy Spirit of God, by whom (we) were sealed for the day of redemption" (Eph. 4:30).
When we tell people that Jesus is the Messiah—that "God has highly exalted him and bestowed on him the name that is above every name" (Phil. 2:9)—and yet we follow after human personalities, what becomes of our witness?
When we condemn greed yet show favouritism to the rich, we deceive ourselves, for "has not God chosen those who are poor in the world to be rich in faith and heirs of the kingdom, which he has promised to those who love him?” (James 2:5).
Those who say they live for the age to come yet actually live for this age “bring the way of truth into disrepute” (2 Peter 2:2).
Similarly, chose who proclaim the cross must actually live out the cross.
To preach the cross without actually taking up your cross results in the message of the cross being "emptied of its power" (1 Cor. 1:17). Those who say they follow Christ crucified yet lord it over those they lead, masquerading as kings, will be revealed by fire, "for the Day will disclose it" (1 Cor. 3:13).
What becomes of the message of the cross if we set aside the grace of God and impose a harsh [legalism] on others? Instead of "One beggar telling another beggar where to find bread," we become bankers passing by beggars, scolding them for their lack of a work ethic.
Rather, our words must be demonstrated by our lives. In this way the church witnesses to Christ Jesus, concerning both his first and second coming, by word and deed.