Improved Pact Weapon spell attack + damage

Question

From Xanathar's Guide to Everything the warlock invocation Improved Pact Weapon allows you to use a pact weapon as a focus for Warlock spells. It also makes your Pact Weapon +1. The DMG under +1 weapon, says:

You have a bonus to attack and damage rolls made with this magic weapon.

My question is, if I use my pact weapon as a focus and cast Eldritch Blast (or any other attack spell), does the +1 to hit and damage from the weapon apply to the spell?

Or does the invocation simply remove the restriction on needing a material component or other arcane focus for spellcasting?

Answer 1

The bonus only applies to weapon attacks.

The text of Improved Pact Weapon states (emphasis mine):

In addition, the weapon gains a +1 bonus to its attack and damage rolls.

Spell attacks and damage aren't attacks made with the weapon, even if it's used as a spellcasting focus for the spell. Further, a spellcasting focus is only used for spells which require material components.

Answer 2

You can't add the +1 from the weapon to a magic attack roll

The SRD says that

Casting some spells requires particular objects, specified in parentheses in the component entry. A character can use a component pouch or a spellcasting focus (found in “Equipment”) in place of the components specified for a spell.

Having your weapon working as an Arcane Focus means that you don't need a free hand to cast spells with material/somatic components.

As for the Spellcasting modifier:

Some spells require the caster to make an attack roll to determine whether the spell effect hits the intended target. Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficiency bonus.

As a Warlock, your attack roll for the Eldritch blast is your Char mod + your proficiency bonus, the +1 on the weapon is irrelevant.

Answer 3

It depends

+1 weapons add 1 to attack rolls and damage rolls made with the weapon. Improved Pact Weapon, similarly, states: "the weapon gains a +1 bonus to its attack and damage rolls". What needs to be determined, then, is whether or not your spell attacks are made or at least can be made 'with' your weapon. That's largely a matter of how spellcasting works in your setting.

It should be noted that the item's role as an Arcane Focus should not in-itself allow the bonus to apply to spells. While that is the plainest reading of the text, 5e is not meant to be played according to its rules text as a corpus but rather with each part of the text somehow existing in isolation. Since that reading involves using two areas of the rules at once, then, and since the rules do not specially call out that doing so will work okay, it is highly suspect, moreso because that would be a departure from the function of such weapons in previous versions of the game, and that usually warrants clear text on the part of the authors.

So, basically, if you can't add the bonus to a spell attack that means that you can't actually meaningfully incorporate your pact weapon into said spell, and if you can then you are making the attack with the weapon, in some sense.