The fastest way into Mosaic 1, JetBlue's base elite tier, is a status match. Hold 
Alaska Atmos Gold (MVP Gold) or 
Southwest Rapid Rewards A-List — both US-based programs — and JetBlue will match you in directly. The match isn't a permanent grant on day one: it opens a three-month challenge window in which you need to earn 10 tiles to lock the status in, the same bar JetBlue sets for reaching Mosaic 1 on your own.
If you'd rather not lean on outside status, JetBlue also sells the door: the 
JetBlue Plus Card and JetBlue Business Card, both issued by Barclays in the US, earn one Mosaic tile per $1,000 spent in a calendar year on either card. Fifty tiles clears Mosaic 1, so $50,000 of spend gets you there with zero flying required. It's slower than a status match, but it isn't a one-time trigger — you can requalify every year, while the airline-status matches only run once per membership. The 
JetBlue Premier Card adds 25 bonus tiles at the start of each calendar year on top of the same $1,000-per-tile rate, cutting the spend needed for Mosaic 1 to $25,000 — though one independent tracker of the program notes that bonus may skip a cardholder's first year, so a new cardholder could need more spend or time than that implies.
Mosaic 2, the silver tier, is more straightforward if you're coming from Delta: a Platinum 
Medallion match is open to travelers anywhere, with no challenge period attached. That's the cleaner silver-tier path — Alaska and Southwest only reach the entry tier, while the Delta match jumps a level higher for the same one-time move. The same three cards also reach Mosaic 2 on spend alone: $100,000 a year on the Plus or Business card, or $75,000 on the Premier Card with its annual bonus, clears the 100-tile bar, repeatable every year unlike the one-time Delta match.
Card spend keeps climbing past Mosaic 2, but status matching stops there — no free match reaches Mosaic 3 or Mosaic 4. Mosaic 3 needs 150 tiles ($150,000 on the Plus or Business card, $125,000 on the Premier Card); Mosaic 4, the top tier, needs 250 tiles ($250,000 on the Plus or Business card, $225,000 on the Premier Card), with no annual cap on tiles earned.
Miles