What was the motive of Jesus in doing his miracles?
Because prophecy would be fulifilled in this way.
Do his miracles invalidate faith in xians because they give what many here at EVC have long asked for: evidence?
If you'll notice from scripture, many, if not most of Jesus' mircales only occured when the people had faith that he could do it. Like the woman who stated, "If I only I touch his cloak, I'll be healed." Or the Centurian who said, "If only you say the word and my servant will be healed." By contrast, the gospels are replete with instances of Jesus not doing many miracles in certain provinces. The number one reason? "And Jesus didn't perfrom very many miracles there because of their unbelief."
I've never seen a miracle, at least not in the classical sense, yet I still believe. Nothing is invalidated. What won't be invalidated is the excuse on that Day when you say you needed 'evidence,' only to hear the Words, "I tell you the Truth, I never knew you. Away from you evildoer."
"There is not in all America a more dangerous trait than the deification of mere smartness unaccompanied by any sense of moral responsibility." -Theodore Roosevelt