“Corroborate” means to “Establish or strengthen as with new evidence or facts. Give evidence for. Support with evidence or authority or make more certain or confirm.” (Wordweb)
When we read of Christ healing a lame man on the Sabbath, we should receive it as the Father’s testimony that he sent the Son, that the Son does what the Father does, and that the Son is equal with the Father, keeping in mind that the Son can only do what he sees is Father doing.
For the sake of trustworthy testimony and the salvation of others—not for his own sake—Christ would not testify on his own behalf without other corroborating testimony. His testimony was part of a package of testimony, all of which God graciously provided so that we may be persuaded, see Christ for who he is, honor him, trust him, and be saved!
As the Old Testament says, a testimony is established by two or three witnesses. When we testify of Christ’s message and identity with the Father, our testimony is not true or valid if we alone testify. All the various sources of testimony should corroborate it. We should model Christ in using all the God-appointed sources of testimony, which all in unison point to the trustworthiness and glory of Christ and his message.
If someone’s testimony about Christ is not corroborated by other testimony, it is not worth receiving. Genuine belief in truth will be supported and encouraged by a varied package of testimony that God has graciously provided.
Those who do not receive the testimony of Christ and his messengers reject multiple sources of reliable testimony. People who are exposed to the beauty of creation, scripture, miracles, the Father, John the Baptist, convictions of the Holy Spirit , the Holy Spirit’s miraculous gifts, transformed lives, historical evidence, reasonable persuasion, archaeology, the love of Jesus, portrayals of the beauty and righteousness of Christ, etc. are afforded multiple sources of trustworthy testimony that point to Christ.
All true disciples and believers of John the Baptist come to Christ, because his words and works pointed to Christ. All true disciples and believers of Moses come to Christ, because the words of Moses pointed to Christ. If you don’t come to Christ, you have tragically missed their point!
The Son is to be equally honored with the Father, because the Son does everything the Father does, and can only do what the Father does. If we do not honor the Son to the degree that we honor the Father, we fail to honor Him as the Father intended. The Father-Son relationship is uniquely worthy of worship and honor and marveling. The miracles and works and words of Christ are meant to bring us to honor them both as God.
Christ is indeed equal with the Father, but the Son nonetheless is in perfect submission and dependence upon the Father. He only seeks the will of the Father who sent him. He only does what he sees his Father doing. Just as the Father has life in himself, so the Son has been granted to have life in himself. The Son’s testimony is reliable because of his perfect submission and dependence upon the Father.
Those who receive the testimony of the Son honor the Father who sent him. They have already passed from death to life. They already have eternal life. The transforming resurrection-life is experienced now. The hour is already here: Christ is resurrecting whom he wills from death to life. The hour is coming: Christ will be the resurrector and judge of mankind. Those who have done evil will be resurrected unto judgment and wrath and condemnation. Those who have done good will be resurrected unto life—not mere existence, but qualitative, Christ-honoring, life-in-abundance.
Those who receive the testimony of the Son will not come into judgment. The present verdict secures the future verdict. Those who have already passed from death to life will be so transformed by the resurrection-life that they will be identified as those who “have done good”. Those who have already been condemned in the present (because of their rejection of reliable testimony), will be identified as those who have “done evil”, having remained in death and under wrath the entire time.
To repeat a D.A. Carson quote:
Eternal life is “the life of the age to come, experienced now even if consummated only later (cf. 5:20-21, 25-26; 17:2)… This does not collapse the notion of [future] judgment into present, spiritual experience, since the future judgment remains (5:28-29). Rather, it is in line with the New Testament insistence that the age to come can no longer be set off absolutely from the present age, now that Jesus the Messiah has come. Believers already enjoy the eternal life that will be consummated in the resurrection of their bodies at [Christ’s second coming]; unbelievers stand under the looming wrath of God that will be consummated in their resurrection and condemnation…” –D.A. Carson, The Gospel According to John, p. 214