The short explanation for warlock blade pact is that if you take the improved pact weapon invocation you can use ranged weapons as your pact weapons (and hex weapons if you are a hexblade), which then means you can also use your charisma modifier to attack with it, and you can eldritch smite through it as well. Alongside this, as you play the character you would naturally aesthetic your spell delivery as being done through your pact weapon as well, so even though you aren't technically shooting spells, you can aesthetic that scorching ray as being bow shots, perfectly legitimately, etc.