The Holy Spirit fell upon them at Pentecost which required Peter to explain to them what it meant. Later he was arrested and the authorities ordered them to cease witnessing. Their answer was "'we cannot stop speaking what we have seen and heard'" (Ac 4:20). "Having the same spirit of faith . . . we also believe, therefore we also speak" (2Co 4:13). Jesus said that you don't shutter your lamp but rather put it "'on the lampstand; and it gives light to all who are in the house'" (Mt 5:15). It is understandable that the apostles would tell everyone because they had just been with Jesus for three years and it was fresh. Then as the years passed the experiences and teaching were written down and you might say it became second-hand evidence. In fact, a Bible school professor told me there are people called cessationists who believe that many of the things which happened through Jesus and the apostles stopped being exercised after their deaths. However, Paul explains "even though we have known Christ according to the flesh, yet now we know Him thus no longer. Therefore if any man is in Christ, he is a new creature" (2Co 5:16-17). "You have been born again not of seed which is perishable but imperishable" (1Pe 1:23). "'Unless one is born of water and the Spirit, he cannot enter into the kingdom of God'" (Jn 3:5). So you are not a second-hand Christian. "'You are the salt of the earth'" (Mt 5:13). Therefore "let your speech always be with grace, seasoned, as it were, with salt" (Col 4:6). However, someone reported that through a study they found that a preponderance of witnessing was done by those who had been Christians for less than a year. That is why Jesus said to the church in Ephesus, "'I have this against you, that you have left your first love. Remember therefore from where you have fallen, and repent and do the deeds you did at first'" (Rev 2:4-5).
Paul explained that Jesus "has committed to us the word of reconciliation. Therefore, we are ambassadors for Christ, as though God were entreating through us . . . be reconciled to God" (2Co 5:19-20). It was so important to Jesus that he said, "'My food is to do the will of Him who sent Me, and to accomplish His work'" (Jn 4:34). Peter recognized God's work as "'to do whatever Thy hand and Thy purpose [has been] predestined to occur'" (Ac 4:28). "It is God who is at work in you, both to will and to work for His good pleasure" (Php 2:13). Paul's goal was to reach "every man . . . [saying] for this purpose also I labor, striving according to His power, which mightily works within me" (Col 1:28-29). He also said "I press on in order that I may lay hold of that for which also I was laid hold of by Christ Jesus" (Php 3:12). Furthermore he asked the Colossians to pray "that God may open up to us a door for the word" (Col 4:3). This demonstrates that they needed God to accomplish their purpose. However, you must still "conduct yourselves . . . making the most of the opportunity" (:5). Jesus pointed out, "'Behold, I say to you, lift up your eyes, and look on the fields, that they are white for harvest'" (Jn 4:35). Do not postpone it. "He who watches the wind will not sow, and he who looks at the clouds will not reap" (Ecc 11:4).