John Calvin on Matthew 16:2

2. About the commencement of the evening. By these words Christ reminds them that his power had been sufficiently manifested, so that they must have recognised the time of their visitation, (Luke 19:44,) had they not of their own accord shut their eyes, and refused to admit the clearest light. The comparison which he employs is beautiful and highly appropriate; for, though the aspect of the sky is changeable, so that sometimes a storm unexpectedly arises, and sometimes fair weather springs up when it was not expected, yet the instructions of nature are sufficient to enable men to predict from signs whether the day will be fair or cloudy. Christ therefore asks why they do not recognize the kingdom of God, when it is made known by signs not less manifest; for this proved clearly that they were excessively occupied with earthly and transitory advantages, and cared little about any thing that related to the heavenly and spiritual life, and were blinded not so much by mistake as by voluntary malice.