Who is the watchman on the wall?

Again the word of the Lord came to me, saying, “Son of man, speak to the children of your people, and say to them: ‘When I bring the sword upon a land, and the people of the land take a man from their territory and make him their watchman, when he sees the sword coming upon the land, if he blows the trumpet and warns the people, then whoever hears the sound of the trumpet and does not take warning, if the sword comes and takes him away, his blood shall be on his own head. He heard the sound of the trumpet, but did not take warning; his blood shall be upon himself. But he who takes warning will save his life. But if the watchman sees the sword coming and does not blow the trumpet, and the people are not warned, and the sword comes and takes any person from among them, he is taken away in his iniquity; but his blood I will require at the watchman’s hand.’ “So you, son of man: I have made you a watchman for the house of Israel; therefore you shall hear a word from My mouth and warn them for Me. When I say to the wicked, ‘O wicked man, you shall surely die!’ and you do not speak to warn the wicked from his way, that wicked man shall die in his iniquity; but his blood I will require at your hand. Nevertheless if you warn the wicked to turn from his way, and he does not turn from his way, he shall die in his iniquity; but you have delivered your soul. (Ezekiel 33:1-9 NKJV)

A watchman discerns (discovers or sees) the coming danger to the people of his land and must blow the trumpet to warn the people of the coming threat or be responsible for their demise in their own iniquity. The Lord is not willing that any should perish but that all should come to repentance.

“What do you think? If a man has a hundred sheep, and one of them goes astray, does he not leave the ninety-nine and go to the mountains to seek the one that is straying? And if he should find it, assuredly, I say to you, he rejoices more over that sheep than over the ninety-nine that did not go astray. Even so it is not the will of your Father who is in heaven that one of these little ones should perish. (Matthew 18:12-14 NKJV)

The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance. (2 Peter 3:9 NKJV)