The scribes and Pharisees had evidence of his power—his many miracles (dunameis—but they refused to see those works as a sign from heaven (sémeion). They demanded a display of divine authority that would validate both his person and message (1 Corinthians 1:22). This was not a request, but a challenge, doubting his right to act as a Teacher in Israel, setting themselves up to judge his authority, treating him with not reverence, but suspicion.
The request for a sign can show unbelief or of little faith: a refusal to bow to the Word (John 20:25). A sign can be asked in faith, after first receiving the Word, or in unbelief, in rejecting the Word—so sometimes God grants a sign in response to such a request, and sometimes he does not (compare Luke 1:18 with Luke 1:34). God also makes use of signs (Moses before Pharaoh, the sacraments) when he deems them necessary: when the spoken Word is of such a kind that he wills to confirm it in view of our weakness.
The scribes and Pharisees wanted to see a sign from Jesus not because they lacked evidence of his power, for he had already performed many miracles (dunameis), but because they refused to accept those works as a true sign from heaven (sémeion). What they demanded was an unmistakable display of divine authority, a proof of legitimacy that would validate both his person and his message (1 Corinthians 1:22). In reality, this was less a request than a challenge: they doubted his right to appear and act as a Teacher in Israel. While the crowds were beginning to wonder if he might be the Son of David, the scribes and Pharisees set themselves up as examiners of his authority, approaching him with no reverence, only suspicion.
That the scribes and Pharisees ask for a sign is not surprising. The request for a sign occurs repeatedly throughout Scripture, as it arises from man’s desire not only to hear but also to see. It can be an expression of unbelief or of little faith—a refusal to bow to the Word (John 20:25). A sign can therefore be asked in faith, that is, after first receiving the Word, or in unbelief, that is, in rejecting the Word. Hence, sometimes God grants a sign in response to such a request, and sometimes he does not (compare Luke 1:18 with Luke 1:34). God himself also makes use of signs (Moses before Pharaoh, the sacraments). He gives them when he deems them necessary, that is, when the spoken Word is of such a kind that he wills to confirm it in view of our weakness.1
38 Then some of the scribes and Pharisees answered him, saying, “Teacher, we wish to see a sign from you.”