Most players I've talked to regard Blessing of Wisdom among the many 1-mana Paladin trash spells, perhaps better than Hand of Protection and Eye for an Eye, but not by enough to see play, even in most aggressive Paladin decks, let alone in standard midrange builds. How Blessing of Wisdom got this reputation I don't know. Sure, this is not a card that by itself will win games; Blessing of Wisdom is never going to be the lead singer or the guitar soloist, or even the drummer — it's more like the bassist, providing consistency and support to help the cards in the spotlight shine a little brighter. But I find it's helpful to have a bassist in the rock band.
This is the midrange Paladin list that I climbed to legend with over the last two days. I started playing it at rank 6 and maintained around a 75% win rate with the deck over ~45 games, beginning with a 16 game win streak to rank 2. It is fairly typical of current midrange Paladin lists, except that it runs two Blessings of Wisdom and one Sea Giant.
The logic behind Blessing of Wisdom is similar to the logic for Flare before it was nerfed from 1 to 2 mana: it is essentially a spell that says "cycle 1 card for 1 mana," with potentially large upside. In the case of Flare, the upside was killing a secret. In the case of Blessing of Wisdom, the upside is the opportunity to draw 2 or even 3 or more cards, and occasionally to prevent an enemy minion from attacking. It is important not to be greedy about Blessing of Wisdom: in most games, it is correct to play it to cycle 1 card, and that is already good enough value. Frequently, Blessing of Wisdom allowed me an extra chance to draw into lethal or the next piece of my curve.
Of any standard archetype, Midrange Paladin has perhaps the most free deck slots. The usual approach is to fill the extra slots with tech cards or additional threats, like Coghammer, Harrison Jones, Sylvanas Windrunner, Bomb Lobber, Captain Greenskin, or Kel'Thuzad. I have experimented throughout the season with a variety of different builds of Paladin, and when I look at the statistics, the clear theme is that in games where I get to play the core Midrange Paladin cards — Shielded Minibot, Muster for Battle, Quartermaster, etc. — I win more. Running Blessing of Wisdom instead of tech cards in effect reduces the deck size from 30 to 28 cards, increasing the likelihood of drawing the core, game winning cards that make Midrange Paladin strong in the first place. I should note that Blessing of Wisdom, while appropriate for aggressive and midrange decks, is counter-productive for the Control Paladin gameplan, which frequently aims to drag games out to fatigue.
I never keep Blessing of Wisdom on the mulligan, since the ideal is to draw a perfect curve. Blessing of Wisdom comes in when I don't draw a perfect curve. Since by definition I'm floating mana already, I can play Blessing of Wisdom more or less for free, hopefully drawing into my curve for the next turn. One player I spoke to aptly called this idea a "lube" card.
I faced few bad matchups on my climb to legend. Even Patron Warrior, which is usually considered to be favored against Paladin, was quite winnable by putting on as much pressure as possible as early as possible. Rogue is probably the worst matchup; to win, you need the Rogue player not to draw at least one of Sap, Fan of Knives, or Blade Flurry. Flamewaker Mage and Face Hunter are both difficult, but winnable with favorable draws. Every other matchup that I faced — which does not include every deck, naturally — I won the majority of the time. My full match history is available at http://goo.gl/qcD3sX (the games start June 20, 4am Pacific).
The best decks are usually the cleanest, tightest lists with little room for extras. I would like to see Midrange Paladin reach that point, and I think Blessing of Wisdom helps that mission.
A quick word about the rest of the deck
Sea Giant is in the list because, in most matchups, this deck wins by putting pressure on the board. It is excellent against Zoo (the most common deck I faced). Against decks with high burst potential, like Druid and Patron Warrior, it helps more than the additional heal of Lay on Hands to close games before the opponent can assemble a lethal combo. Sea Giant has obvious synergy with Muster for Battle — conveniently, since Muster for Battle spawns 3 minions, Muster for Battle + Sea Giant costs the same as Sea Giant alone. Sea Giant also has strong synergy with Emperor Thaurissan, since Emperor Thaurissan not only decreases the cost of Sea Giant itself, but also decreases the cost of every other minion in hand, effectively decreasing the cost of Sea Giant again for every minion that can be played. In the mirror matchup, you can sometimes get Sea Giant out very early, but beware of Aldor Peacekeeper.
I ran double Quartermaster for a while, but one Quartermaster and one Sea Giant proved to be more consistent.
Solemn Vigil is much faster than Lay on Hands and fits better with the gameplan of consistent pressure.
I experimented with Argent Squire instead of Zombie Chow and found that it was quite good, but Zombie Chow proved to be more consistent against the decks I faced. The ability to trade favorably is more important than the extra Divine Shield synergy with Blessing of Wisdom — remember, Blessing of Wisdom is just a lube card, not a win condition. The consistency of two 1-drops is more important than the late-game drawback.
One Knife Juggler is excellent with Muster for Battle, Equality, and Dr. Boom, but two would be weak, since Knife Juggler is so vulnerable in the early game.
I think it is important to run 1 each of Defender of Argus and Piloted Shredder, because sometimes you want a solid minion on curve, and other times you want to get value or burst out of protecting/buffing 1/1 tokens.
Lack of burst damage has traditionally been a major shortcoming of Paladin, and Blessing of Kings helps to remedy that. Since it is much better as a finisher than in the early game, I almost never keep Blessing of Kings on the mulligan.
I stopped to write after reaching legend, but I will continue to ladder with this list as long as I keep winning with it. I hope you will find as much success with it as I have had.