Balance options that make it better, but not too good (these are alternatives added to the existing spell):
1.) Make the duration 3 rounds (concentration).
2.) Make the casting time a bonus action, but don't allow it to be cast if you've moved this turn, and have it end if you move.
3.) Make the casting time a reaction based upon being attacked - have it last until the start of your next turn.
4.) As a reaction, you inflict (ability score modifier) radiant damage on an adjacent target that misses you with an attack.
5.) Damage resisted is added to the damage inflicted on one target of your choice that is damaged by the next spell you cast before the end of your next turn.
6.) A target that misses you with a melee weapon must make a Wisdom save versus your spell DC or their weapon flies from their grasp and travels (d4-1) spaces in a random (d8) direction (1 forward, 2 forward and right diagonally, 3 right, etc...)
Those are lots of interesting ideas. I do see some problems with them, though.
1)This certainly works. Maybe a bit too well? What fighter wouldn't give up his action surge for 3 rounds of taking damage like a barbarian, while still using heavy armor and dishing out his battlemaster tricks? I can't see him caring much about it taking concentration (unless he fails that and the Ward goes away). Eldritch Knight 7th level would take it for sure and become a magic-slinging barbarian. Although, yeah...concentration. Still, this seems like a real death-knell for Stoneskin.
2)Similar problems as above. Probably even better for battlemaster, since you don't lose anything important (just avoid maneuvers that use your bonus action) and get cost-free and endless damage resistance. I think this is probably plain OP.
3)Even more OP. Just avoid Riposte, and let the caster behind you know that he's on his own if the baddies flow around you unimpeded.
4)You lost me. How is this Blade Ward? It sounds like an awesome reaction cantrip for when you're all out of Shields and Counterspells, and have nothing to do with your reaction anyway (well, Warcaster I guess. But who runs AWAY from the wizard?). But what's it got to do with damage resistance? Sounds like a Heckish Rebuke.
5)Hmmm. So, my wizard 5 gives up his action when he's cornered by a fighter, takes say 20 HP damage and resists 20, then next turn he smashes the metal-lined tank with a melee-spell-attack-at-advantage Shocking Grasp dealing 2d8 + 20 damage before running off without an Opp Attack? All without burning a spell slot to save himself? Guess that fighter won't try that again! Seriously, the wizard comes out of that a little too well off in my opinion without having to cast a real defensive spell (Mirror Image/Misty Step/Shield/Whatever). Sounds, maybe...a little too good? Personally, I think casters are a bit too good in combat as it is. I'm old school like that.
6)Huh. Think I kinda like that. Maybe a Str save, though?
Anyhow, some cool ideas. Yours are way more creative and better than any idea I have on the subject. But I think many others have said it before: b/s/p resistance (including magic weapons, apparently) is pretty powerful. Letting somebody have it endlessly and without cost as a cantrip needs to have some serious drawbacks like the current Blade Ward, or it's way too easy to make it OP.