Our modern appreciation of symbolism is not always as strong or as vivid as that of people of Jesus' time. On the other hand, we do have our own way of symbolizing things and of appreciating symbolism, even if such appreciation is often somewhat unconscious. Thus, when we watch a movie, the colours and the background music all play a part in our appreciation of what the movie is trying to tell us. If we apply this appreciation of symbolism to the prophecy of Ezekiel, we will derive a greater meaning from his rich symbolism.
Thus, Ezekiel stands outside the Temple: he is symbolically an "outsider", a Gentile. He sees water flowing from the entrance, from under the threshold. It is not a trickle of water, it is not a shower of rain but water flowing like a river from the Temple. If water symbolizes God's saving grace, both for those inside and outside Judaism, its strong flow symbolizes the abundance and the power of that grace.
The water flows in the same direction in which the Temple is facing: God's grace, whenever given, will accomplish everything that the Temple signified and accomplished in Judaism. God is with us with abundant saving grace giving life as water gives life.
Refresh our lives each day, O Lord, through the saving waters of Your grace.