Episode 3 - The Hunted
Having a Paladin for each Lion isn't all that's required to form Voltron. What's needed is a team that works together as a cohesive unit - something that this team is so far incapable of doing. Having placed a tracker on Lotor's ship, Keith decides they should pursue it and take out Zarkon's heir now. It's an impulsive decision, but then that's Keith.
His foolish decision only ends up creating more opportunities for Lotor, who chooses to fly out alone and face the Paladins himself. And while the ensuing battle makes for some striking action, it only exposes how terribly out of sync the Paladins are with each other and their lions. Keith isn't leading but trying to take on Lotor all by himself; Lance isn't helping but rather harping on Keith's poor leadership; and Allura isn't listening, ignoring any of the advice her fellow Paladins offer. In short, they're a total mess.
Realizing how inept they are, Lotor devises a trap in where he leads them to a planet engulfed in a storm which will distort their sensors. Flying basically blind, their inability to work as a team ends up with everyone separated - a literal representation of their own shortcomings as a team. In the end, it's Allura, their newest member, who bonds more closely with the Blue Lion to reveal a new sonar ability that she uses to track down her missing teammates. And it feels right for it to be Allura that brings them together - not only was that her initial role in the series, pairing the Paladins with their Lions, but as the one most unfamiliar with being part of a team it's she, not Keith or Lance, who has the biggest personal hurdle to overcome: learning to ask for help. (We also get her hysterically accurate impression of Lance as an added bonus.)
This breakthrough for Allura leads to a most satisfying moment in which she's able to get the upper hand on Lotor, displaying impressive skill for a newly minted Paladin. She also has a great line when the team finally unites to form Voltron - "Hunk, I'm a leg!" - and that enthusiasm, along with how they absolutely wreck the Galra ships Lotor called in for back up, are a strong indication that this Voltron team is finally on the right track.