7:17 for the Lamb in the center of the throne shall be their shepherd, and shall guide them to springs of the water of life; and God shall wipe every tear from their eyes."

for the LAMB in the center of the THRONE shall be their SHEPHERD,

Here are all these horribly persecuted, physically hungry and thirsty saints seeing Christ the LAMB Himself being their SHEPHERD; this isn't assigned to some group of angels; it wasn't part of the 4 living creatures jobs; it is the LAMB Himself to be their SHEPHERD. So what does a shepherd do?

and shall guide them to springs of the WATER OF LIFE;

When these saints were hiding from AntiChrist authorities, they were on their own - intuition was their guide along with a complete faith in Christ. Now their faith yielded results. The SHEPHERD takes responsibility to GUIDE them.

The water of life is a whole topic unto itself. We find it

and God shall wipe EVERY TEAR from their eyes.

These saints must have gone through horrible events: torture, seeing loved ones killed, compassion of others to give them food and water, and on and on. But GOD Himself (not the LAMB) will remove all the tears.

Mercifully, the remembrances of bad times will be removed from their minds. There will be no tears in the new heaven, Revelation 21:4. The Lord God will throw a lavish banquet for all peoples (the marriage supper), Isaiah 25:6-12. Isaiah also reminds us what it will be like in the new heavens, Isaiah 65:17-19-25, where there will be no voice of weeping and no sound of crying. JOY replaces the sorrow and weeping, Psalm 16:5-11.