I do not know about you but the WCF has an article on assurance but it does not help assure, at least it would not help assure me or it has failed to assure me.
I refer you to Article XVIII, but we do not need to go far, just the first one will do and you will see what I mean...
I. Although hypocrites and other unregenerate men may vainly deceive themselves with false hopes and carnal presumptions of being in the favor of God, and estate of salvation (which hope of theirs shall perish): yet such as truly believe in the Lord Jesus, and love Him in sincerity, endeavouring to walk in all good conscience before Him, may, in this life, be certainly assured that they are in the state of grace, and may rejoice in the hope of the glory of God, which hope shall never make them ashamed.
Now this is precisely the point, when a person is doubting and even in the state of depression, he precisely does not have what these qualities, can you get me?
I mean, firstly the person in a crisis doubts everything in himself, he does not know if he believes in Jesus, he looks at himself and compares it with this article and he says he does not think he loves Him, he doubts if he is even walking in all good conscience for doubt itself is not a good thing...
I will cut to the chase, it will fail to assure because it talks about inward qualities and those qualities are really not there in a person who is in a critical period of their walk in the Christian life. Then because Jesus only died for the elect (as Calvinism states aka Limited Atonement), he can not look outside either because there is nothing out there to hold on, the promise of God is not for you necessarily it is only for the believer, but that is exactly what you are doubting if you really are!!! So it leads to dispair.
The only thing that can break that is the passage of Scripture like 1 John 2:1-2. What we need is a promise of God to the sinner first, then to the believer, this is answered by objective justification.
Ok I got to run, have a good weekend and if you want to enjoy God and glorify him forever, look at your sin and then look at your Saviour (I hope to say more on Piperian Hedonistic Christianity next time).