(The Opener / The Judge)
The Opener, the reliever, the judge. He is the one who opens the hearts of His slaves and holds the keys to success in this world and the hereafter.
Al Fattah is the opener, the revealer, and the granter of success. He opens or locks His doors of mercy to whom He pleases. Through his guidance whatever is unclear becomes clear. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ has the best judgment and holds the keys for victory and success.
From the root f-t-h (ف-ت-ح) which means to open. It has the following classical Arabic connotations: to open, unlock, unfold, to make victorious, to reveal, inform, explain, make clear, to judge, to decide, to grant, and to permit.
There are multiple meanings associated with this name. In Arabic, fath (فتح) means to open, and al-Fattah (ٱلْفَتَّاحُ) is the opener. It describes Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ with a perpetual form that is ever-lasting. He is the one that is always doing this again and again. Now, what is implied by opening? What is that He opens? As we covered in the last name, Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ holds the key to our sustenance (ar-Razzaq), so naturally, He is considered the opener to provisions.
He is also the one who opens the door of mercy. Narrated by Abu Huraira who reported Allah's Messenger ﷺ as saying: When it is the month of Ramadan, the gates of mercy are opened, and the gates of Hell are locked and the devils are chained. 
It can also mean providing guidance to one who is lost, revealing the unseen, a path untrodden. Sometimes we see things as impossible. Our minds were unable to see it in a different light. But that is until Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, in all His glory, clears our minds and opens the possibility for us. We are blinded and unable to see, i.e., until He reveals. So, we learn that al-Fattah is the one who makes what was once impossible possible.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ also opens the doors to His tests, for both the believers and those who don't believe. He may open the access to fame, wealth, or power just to see how we respond. For others, he may take it away. In the Qur'an it mentions, "So when they forgot that by which they had been reminded, We opened to them the doors of every [good] thing until, when they rejoiced in that which they were given, We seized them suddenly, and they were [then] in despair." (Qur'an 6:44)
Moving onto the instances of the name al-Fattah as mentioned in the Qur'an. It appears only once; however, many verses exemplify this attribute of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. Below is the ayah in which this name was revealed.
Say, "Our Lord will bring us together; then He will judge between us in truth. And He is the Knowing Judge."(Qur'an 34:26)
The believer benefits in knowing al-Fattah. By being vulnerable oneself, by opening up towards Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ you give yourself the opportunity for Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ to open His doors of mercy for you. Abu Hurairah narrated that the Messenger of Allah ﷺ said: "Indeed Allah Most High says: 'I am as My slave thinks of Me, and I am with him when He calls upon Me.'" 
From this name we further recognize that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the only one we need to rely upon. Whatever it is we need access to, al-Fattah is the one who can open it for us. If you're feeling stuck, unable to make a decision, ask Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ to open your heart to make the right choice. He is the best judge who knows whether a thing will be a benefit for you in your deen, in your relationship, or your livelihood.
The Prophet ﷺ recommended that when we enter the masjid we should make this du'a, اللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ Allahumma-iftah li abwaba rahmatik which means, "O Allah! Open for me the gates of Your mercy!"  This is a beautiful du'a which keeps in mind that when we enter a masjid we're seeking to experience Allah's mercy. This dhikr is remembrance of the fact, it directly asks Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ to open His gates of mercy for us.
The hadith then continues, And when he leaves (the masjid), let him say: اللَّهُمَّ إِنِّي أَسْأَلُكَ مِنْ فَضْلِكَ "Allahumma inni as'aluka min fadlika., meaning "O Allah, I ask of you from Your bounty."The parallel, when you enter a masjid seek his mercy, look towards your afterlife, but when you leave, seek his grace, and bounty so that you can be successful in this Dunya.
"Whatever Allah grants to people of mercy – none can withhold it; and whatever He withholds – none can release it thereafter. And He is the Exalted in Might, the Wise." (Qur'an 35:2)