Guiding Bolt

The power-4-or-greater clause is doing double duty here: it narrows the removal so it can't touch the small threats white already answers cheaply, and it aims the card squarely at the fatties white historically struggled to kill. That restriction is what pays for the price. Unconditional instant-speed creature removal at this rate would be a design outlier for white, so the spell is priced against a body worth the cost, and it rewards you for waiting until the board actually threatens rather than firing at a mana dork. The scry is the second wrinkle, but not because it saves the card when there's nothing to kill: the spell needs a legal target to cast, so if the big threat never shows, this sits dead in your hand like any other conditional answer. What the scry does instead is smooth the turn you finally get to fire it. You've been holding the card, sculpting nothing else while you waited; when the threat lands and you kill it, the top-two dig hands you a partial refund on that patience, digging toward your next play at the exact moment you've spent a card reacting. That pairing (a conditional kill stapled to card selection) is a recurring shape in white's answer suite, and it works cleanly because the two halves address the same problem: the condition asks you to hold, and the scry makes the payoff for holding feel less like tempo lost.