The difference between them is plain for all to see—
perceived by anyone granted a portion of true insight.

In short, the contrast between the two bā’s is this: Paradise is only gained and entered by Allah’s mercy, while the bā’ that appears in the relevant texts functions as a marker of causation. The Messenger of Allah ﷺ ruled out entry on account of deeds when he said, “None of you will enter Paradise by his deeds” (al-Bukhari 5349; Muslim 2816); here the bā’ signifies “price.” Hence, there is no contradiction between the two statements.