Hi, I have a question. I'm in Morrowind and I found a spell for sale at a Mages Guild trader a spell called Lock 10pts for 1 sec on Touch, school Alteration. I have already used the Open spells to open chests and doors. Is the lock spell used to lock doors and chests? Is it required for a later quest?

The AI won't follow you through closed doors anyway (without mods), so the Lock spell is only useful for practicing lock picking. Cast the spell on a chest, unlock it with your handy lock picks, then repeat until both your Alteration and your Security skills improve, or you run out of lock picks.

The AI can open doors from room to room, but not cell to cell. I've occasionally opened a door, saw a Greater Bonewalker, slammed it shut, and locked it with a spell.

Thank you

In this case, I won't bother at all with this spell, I don't want to level skills too fast by repeating actions.

It's quite useful for security training. Lock a chest/door and try unlock it with your spare low level picks. Your security skill will start growing, giving you a chance to level your intelligence attribute as well.

Kovacius is partially mistaken. The AI won't follow you into new cells through a loading door but they will open doors that swing open and shut inside the cell you are in, so the Lock spell is very useful for locking doors that are internal to the cell. The AI can open those doors and will go through them, so if they are chasing you and you can close and lock a door quickly enough, you can escape enemies with the Lock spell.

I am inclined to believe that Kovacius meant "doors that transport to a new cell" when he wrote "closed doors." He just didn't specify it.

If that is what he meant then why did he also write that "the Lock spell is only useful for practicing lock picking"? It clearly has a use to stop enemies from pursuing you though doors that do not transport you to a new cell, which are not terribly uncommon in Morrowind.

My characters have used it to great advantage when they want to visit ancestral tombs for blessings but were not strong enough to defeat the undead that lurked deeper within, so they blocked them off at the swinging door with a simple lock spell.

Tbh I never thought people may actually use the locked spell in real combat scenarios besides the aforementioned skill grinding. Not even in Skyrim where npcs have mobility I wouldn't use it just to avoid combat. Sooner or later I'd have to get out and the enemy would still be there. A great use of a locked spell would be if there would be npc thieves with various open skills who can steal from the player's chests and breakingbinto my home. Setting physical and magical traps and hard locks to keep my valuables protected, and finding a thief or assassin near the locked door or chest, killed by the trap or spell, would be somewhat entertaining.

It doesn't even need to be a strong lock spell since the AI can't use security. You can stop an army dead in their tracks with a one point lock.

Morrowind was a lot more brutal than Oblivion or Skyrim with attribute damage. Those Greater Bonewalkers were nasty.