The previous verse says that Herod put John in prison. It might be helpful to make it clear that the account starting in verse 21 happened before John was arrested. The UDB does this by starting verse 21 with "But before John was put in prison." (See: [[rc://en/ta/man/translate/figs-events]])
This phrase marks the beginning of a new event in the story. If your language has a way for doing this, you could consider using it here. (See: [[rc://en/ta/man/translate/writing-newevent]])
"while John baptized all the people." The phrase "all the people" refers to the people present with John. (See: [[rc://en/ta/man/translate/figs-activepassive]])
"the sky opened" or "the sky became open." This is more than a simple clearing of clouds, but it's not clear what it means. It possibly means that a hole appeared in the sky.