Although there are a few scattered references to Jesus in contemporary secular writings, especially in Tacitus and Suetonius, the main source of our information about him remains the four "Gospels." They are rightly so called. For strictly speaking they are not biography, but testimony. They bear witness to Christ and to the good news of his salvation. Therefore their authors select, arrange and present their material according to their purpose as "evangelists." This gives us no ground to doubt their trustworthiness, however. On the contrary, we should approach the Gospels with confidence, not suspicion. There are many reasons for doing so.
First, the four evangelists were certainly Christian men, and Christian men are honest to whom truth matters.
Second, they give evidence of their impartiality by including incidents they would clearly have preferred to omit. For example, although by that time Peter was a highly respected church leader, neither his boastfulness nor his denial of Jesus is suppressed.
Third, they claim either to be themselves eyewitnesses of Jesus or to report the experience of eyewitnesses. Although it seems likely that no Gospel was actually published earlier than AD 60, we must not imagine that there was an empty gap between the ascension of Jesus and that date. This was the period of "oral tradition," in which the words and deeds of Jesus were used in Christian worship, evangelism and the teaching of converts, and so began to be collected in writing. Luke says he drew on "many" such compilations (Luke 1:1-4).
Fourth, Jesus seems to have taught like a Jewish rabbi. He gave his instructions in forms (for example, parables and epigrams) which a tenacious oriental memory would have had no difficulty in learning by heart, and in addition he promised that the Holy Spirit would stimulate the apostles' memory (John 14:25-26).
Fifth, if God said and did something absolutely unique and decisive through Jesus, as Christians believe, it is inconceivable that he would have allowed it to be lost in the mists of antiquity. If he intended future generations to benefit from it, he must have made provisions for it to be reliably reported, in order to make the good news available to all men in all times and places. What he decided to do was to present the one gospel in four Gospels.