19 “Your way is in the sea”. But now Your way was in the Holy One, now “Your way is in the sea:” because the Holy One Himself is in the sea, and with reason even did walk upon the waters of the sea. “Your way is in the sea,” that is, Your Christ is preached among the Gentiles....“Your way is in the sea, and Your paths in many waters,” that is, in many peoples. “And Your footsteps will not be known.” He has touched certain, and wonder were it if it be not those same Jews. Behold now the mercy of Christ has been so published to the Gentiles, that “Your way is in the sea. Your footsteps will not be known.” How so, by whom will they not be known, save by those who still say, Christ has not yet come? Why do they say, Christ has not yet come? Because they do not yet recognise Him walking on the sea.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)