‘Now when he had spoken a Pharisee asks him to dine with him, and he went in, and sat down to meat, and when the Pharisee saw it, he marvelled that he had not first drenched (baptizo) himself before dinner.'
It may well be that Jesus had deliberately refrained from ceremonially washing his hands here in order to introduce the subject matter of His speech, for Mark 7:2 suggests that He usually conformed to that requirement (unless Mark 7:2 was a polite way of indirectly hinting that He also had not done so). The point, however, that Luke is stressing is the emphasis of the Pharisee on outward observance. To them it mattered not what inward sins Jesus had brought with Him (like the inward sins of Luke 11:53-54) as long as He was following the correct rituals. (Luke is basically hinting that the attitude of some of the Pharisees was such that they could, as it were, happily connive in the killing of the prophets (Luke 11:47-51), as long as they did it with clean hands).
‘He marvelled.' This may mean that he said something (but compare Luke 20:26), although not antagonistically (see Luke 4:22; Luke 7:9; Luke 8:25; Luke 9:43; Luke 11:14; Luke 20:26), for Luke does not add ‘within himself' (contrast Luke 7:39).
The ceremonial ‘washing of the hands' before eating was one of the tenets of the Pharisees on which they laid great stress. It was not enjoined in Scripture but was an additional element added by the Traditions of the Elders, the oral Law. It was not strictly a simple hand washing, but a ritual mini-ceremony. They believed that because of the possibility of unknown contamination by persons who were ritually unclean it was necessary to wash both before every meal and in between courses. And this involved a complicated process. The water for washing had to be taken from large stone jars which had been kept ‘clean' so that the water itself was kept ritually clean. Such water could be used for no other purpose. First all dirt had to be removed. Then the hands might be held with the fingers pointed upwards and water was poured over them and had to run down to at least the wrist. After this, while the hands were wet, each had to be cleansed, seemingly with ‘the fist' of the other, probably by the joint action of rubbing the palm over the fist. But the water on their hands was now unclean so the hands were then held downwards and water poured over them again so that it began at the wrists and ran off the end of the fingers. That was one way of doing it.
Alternately this might all be done by dipping the hands up to the wrist in a vessel containing clean water, again apparently rubbing on ‘the fist'. Then the hands would be clean.