Priest is the class where the interesting change is not in the trees. Its three trees gained 13 talents and lost 7, which is ordinary. Its ability list gained 40 rows against Era, the most of any class, and nine of those are abilities the Classic Priest simply does not have.
Game data from build 1.60.1.69913 against Era 1.15.9.69722. The trees are in the Priest calculator.
Nine abilities Classic Priests do not have
| Ability | First learned | Line | Ranks | What it does |
|---|---|---|---|---|
 Confounding Flash | 10 | Discipline | 1 | Confuses up to 5 enemies within 8 yards for 3 sec; any damage taken breaks it |
 Divine Grace | 10 | Holy | 7 | Instantly heals a friendly target below 50% health and removes Weakened Soul from them. Cannot be cast on yourself |
 Chastise | 20 | Holy | 5 | Holy damage and an immobilise of up to 2 sec, Humanoids only, very low threat |
 Contingency Plan | 20 | Discipline | 5 | A 30-second ward; when the ally next drops below 35% health it absorbs damage and heals them over 15 sec |
 Dark Sacrifice | 20 | Shadow Magic | 5 | Trades your own health for mana over 15 sec, 400 for 400 at rank 1 |
 Binding Heal | 25 | Holy | 6 | Heals the target and you for 223 to 271 at rank 1, low threat. Also the 16-point Holy talent |
 Penance | 30 | Discipline | 4 | 81 Holy damage or 184 healing, instantly and every second for 2 sec. Also the 21-point Discipline talent |
 Shadow Word: Death | 32 | Shadow Magic | 4 | 286 to 304 Shadow damage at rank 1; if it does not kill the target you take backlash equal to 10% of your maximum health |
 Prayer of Mending | 40 | Holy | 3 | A heal that fires the next time the target takes damage and then jumps to another party or raid member, up to five times. Also the 31-point Holy talent |
Four of the nine are talents as well as abilities, which is how the trees pay for them; the other five arrive on their own.
Divine Spirit no longer costs a talent
Era’s Discipline tree has Divine Spirit at the 21-point row, and the talent and the level-30 ability are the same spell. Forever has no such talent and the ability row is unchanged. Its duration went from 30 min to 60 min at the same time, as did 
Power Word: Fortitude, which also went from +3 to +4 Stamina at rank 1.
That 
Divine Spirit is therefore learned at 30 without a talent is our reading. It matches the pattern Blizzard confirmed for the Paladin’s Consecration, where the talent was removed and the ability row and level kept, but Blizzard has said nothing about Divine Spirit.
Prayer of Healing is a different spell
Prayer of Healing in Era heals party members within 30 yards of the caster for 301 to 321 at rank 1. In Forever it heals the target and the target’s party for 172 to 184, and the party has to be within 40 yards of the target rather than of you. It is a heal you cast on someone else’s group now.
The rest of the spellbook
28 abilities the Priest already had read differently in this build. The ones that change behaviour rather than a number:
| Ability | Era | Forever |
|---|---|---|
 Elune's Grace | −21 ranged damage taken and +10% dodge for 15 sec | −50% chance to be hit by melee and ranged for 15 sec or three misses |
 Hex of Weakness and  Touch of Weakness | Reduce damage caused by a flat 2 | Reduce melee attack power by 43 |
 Fear Ward | Lasts 10 min | Lasts 3 min |
 Starshards | 84 Arcane damage over 6 sec | 162 |
 Levitate | Cancelled by damage | Cancelled by damage or by mounting |
Most of the rest are downward retunes of the healing and damage tables: 
Flash Heal rank 1 heals 174 to 214 against Era’s 193 to 237, 
Heal rank 1 heals 270 to 312 against 295 to 341, 
Holy Fire rank 1 deals 51 to 65 against 78 to 98, 
Devouring Plague rank 1 deals 128 over 24 sec against 152, and 
Renew rank 2 heals 75 over 15 sec against 100.
The three trees in numbers
| Tree | Talents | Ranks | Era talents | Not in the Era tree | In Era, not here | 16-point talent |
|---|---|---|---|---|---|---|
| Discipline | 18 | 51 | 15 | 7 | 4 |  Soul Warding |
| Holy | 17 | 48 | 16 | 3 | 2 | Binding Heal |
| Shadow Magic | 18 | 49 | 16 | 3 | 1 |  Vampiric Embrace |
The Shadow tab is called Shadow Magic in Forever; Era calls it Shadow. Shadow is also the most rearranged tab in the class: eleven of its talents changed tier, rank count or prerequisite while only one left and three arrived.
What is new in each tree
Discipline is where the new talents cluster. Power in Light (5 ranks) gives Smite and Penance 2% to 10% more damage against a target burning from your Holy Fire. 
Twin Disciplines (5 ranks) adds 1% to 5% damage and healing to instant-cast spells. 
Holy Precision (3 ranks) is 6% to 18% Holy spell hit. Soul Warding is the 16-point talent: 4 sec off the Power Word: Shield cooldown and 15% off its cost. 
Renewed Hope (5 ranks) makes your direct heals crit more on targets carrying Weakened Soul and strip 1 to 5 sec off that debuff. 
Divine Aegis (3 ranks) turns critical heals into a shield worth 5% to 15% of the amount healed. Power Infusion now requires Penance rather than Mental Strength.
Holy gained Binding Heal at the 16-point slot, Prayer of Mending at 31 points in place of 
Lightwell, and 
Litany of Light (2 ranks), which refunds 5% or 10% of a heal’s base cost when it is a different spell from your last one.
Shadow Magic gained 
Improved Mind Flay (2 ranks), which adds 10% or 20% Mind Flay damage and 5 or 10 yards of range at the cost of the slow dropping from 50% to 35% or 20%; 
Devouring Contagion (2 ranks), which halves the cost of Devouring Plague and makes it jump to a nearby enemy when its victim dies; and Early Demise (2 ranks), 15% or 30% Shadow Word: Death critical chance against targets below 20% health.
Same name, different effect
| Talent | Tree | Era | Forever |
|---|---|---|---|
 Twilight Focus | Holy | 70% chance to avoid interruption while casting a healing spell, 2 ranks, under the name Healing Focus | The same 70% while casting any spell, 3 ranks, under the name Twilight Focus |
 Improved Inner Fire | Discipline | +30% Inner Fire armour | +45%, and 12 more charges |
 Improved Healing | Holy | Lesser Heal, Heal and Greater Heal | The same, plus Penance and Prayer of Mending |
 Searing Light | Holy | +10% Smite and Holy Fire damage | +5% to all your Holy damage, plus a 10% chance of a free Holy Nova each time Holy Fire ticks |
 Spiritual Guidance | Holy | Up to 25% of Spirit added to spell damage and healing alike | 25% of Spirit to healing, 8% to damage |
 Mental Agility | Discipline | Instant-cast spells, 5 ranks to 10% | Smite, Holy Fire and instant casts, 3 ranks to 10% |
 Shadow Weaving | Shadow Magic | Up to 100% chance over 5 ranks | The same 100% over 3 ranks |
 Shadowform | Shadow Magic | +15% Shadow damage, −15% Physical damage taken, no Holy spells | +10% Shadow damage, −50% Shadow mana cost, +100% Shadow critical damage, −15% Physical damage taken, no healing spells |
What left the trees
Discipline lost Unbreakable Will, Improved Power Word: Fortitude, Divine Spirit and Force of Will. Holy lost Improved Prayer of Healing and Lightwell. Shadow lost Improved Vampiric Embrace. Seven in all, against thirteen that are not in the Era tree.
Beta state
Blizzard’s Known Issues thread for September 17 lists one Priest entry: the Night Elf racial Starshards does not benefit from the Twilight Focus talent (Blizzard Forums: Beta Known Issues – September 17). Given that Twilight Focus was widened from healing spells to all spells in this build, that is the kind of thing the change would break.
The beta cap is 20, rising to 30 later (Blizzard: Beta Now Live). Of the nine new abilities, only Confounding Flash, Divine Grace, Chastise, Contingency Plan and Dark Sacrifice are reachable at that cap.
Not settled yet
Coming soon The absorb and healing figures on Contingency Plan, and the heal on Prayer of Mending. Both spells leave those numbers unfilled in the game’s own text for this build.
Coming soon The stack limit on Shadow Weaving, which the tooltip also leaves unfilled.
That these trees are the ones a Forever character spends points in is our reading of the beta build, not something we have confirmed in game. The reasoning is in Forever talent trees.
Changelog
1- First version, from the game data of build 1.60.1.69913 compared with Era 1.15.9.69722.
