Can't we just preach to or heal anyone?
Jesus had direction to preach to the Jews first and then the Gentiles, but one Canaanite woman managed to break that.
21 After going out from there, Jesus went to the region of Tyre and Sidon. 22 A Canaanite woman from that area came and cried out, “Have mercy on me, Lord, Son of David! My daughter is horribly demon-possessed!” 23 But he did not answer her a word. Then his disciples came and begged him, “Send her away, because she keeps on crying out after us.” 24 So he answered, “I was sent only to the lost sheep of the house of Israel.” 25 But she came and bowed down before him and said, “Lord, help me!” 26 “It is not right to take the children’s bread and throw it to the dogs,” he said. 27 “Yes, Lord,” she replied, “but even the dogs eat the crumbs that fall from their masters’ table.” 28 Then Jesus answered her, “Woman, your faith is great! Let what you want be done for you.” And her daughter was healed from that hour.Matthew 15:21-28
While conservatives tend to operate from presumption that God wants us to preach to anyone and everyone, Jesus didn't operate like that. He operated under direction from the Father. He was to preach to the Jews, and then let the disciples preach to the Gentiles all over the world. This was one exception that proves the rule.
Pentecostals are a bit more nuanced and sometimes ask God about who they should witness to. What this does is that they work with the Spirit, who is the only one who can convict, deliver and save. This is operating under God's direction. The idea is that you look to where the Spirit is already in operation, and follow Him there.
We will later see the disciples wait for the Holy Spirit before witnessing (Acts 1), and then even with the Holy Spirit, they will be directed to the Gentiles (Acts 10), and then even with the Gentiles, they were directed to certain places to preach (Acts 16:6-10). Mature Pentecostals will also be open to changing what they say in light of the Spirit's direction in the moment of speaking (Matthew 10:19-20).
To answer the question directly, I don't think it's wrong to just preach to or heal anyone, unless we've been told specifically by the Spirit. However, we know that unless the Spirit moves, the non-Christians are not going to be convicted or open to the things of God. So it's not going to be effective. In the Matthew passage, the Canaanite woman had great faith in Jesus, so was able to cut through Jesus' general direction.
However, it is clear cut to say that it is wrong to claim that God always wants to heal and save and deliver. Some will be and some won't. To claim that God always wants to heal doesn't even come close to fitting with a general overview of the biblical timeline, where we are expecting perfection only after Jesus comes back. Until then, we will see many glimpses, reflections, metaphors, and reminders—but they'll point towards a future new heaven and new earth. (See series Mission of the Church)
Aren't all the promises of God yes and amen to us in Christ, and therefore we have God's direction and will already?
There is a verse which seems to legitimise the view that we have God's direction on everything already—that he wants you to receive every blessing right now:
For all the promises of God find their Yes in him2 Corinthians 1:20, ESV
The simple answer is that this verse says no such thing. What it is saying is that all the promises of God are fulfilled in Christ.
However, even if it were to say that we could basically expect full blessing and perfection in this lifetime, there is no indication these things are promised at your whim. Perhaps you need to go through a Job-like experience before you will get it. Health and wealth 'gospel' preachers gloss over that.
Consider the most blessed people in Scripture: are they not also the people who experienced the worst suffering imaginable? Joseph, before he became prime minister of the entire Egyptian empire, was unjustly sold and imprisoned probably for twelve yearsHow long was Joseph in prison?, 4/01/2022, Got Questions, https://www.gotquestions.org/Joseph-in-prison.html; Jesus, before he was exalted to the highest place, was crucified; Paul, an Apostle who wrote half the New Testament, was brutally treated many times (2 Corinthians 11:23-29); in fact, it is said that all the Apostles except for John were martyred. Of course, full perfection would surely include no death—and no health preacher has ever overcome that: even those who rise from the dead die sometime later.
Consider now the people who experience the most miracles in life today. They are usually the ones who are the most needy. Who are desperate and have no one else to turn to other than God. Westerners have many other opportunities, and so have come to rarely turn to God: even as Christians. Perhaps instead of seeking blessing for ourselves, we ought to be open to God's direction to dangerously proclaim and demonstrate his name in the world.
Can we prophesy life and abundance to anything?
This blessing-seeking (previous question) is very similar to the idea that we can prophesy to things and people. This comes from Ezekiel 37.
Ezekiel 37:1-14The hand of the Lord was on me, and he brought me out by the Spirit of the Lord and set me in the middle of a valley; it was full of bones. 2 He led me back and forth among them, and I saw a great many bones on the floor of the valley, bones that were very dry. 3 He asked me, “Son of man, can these bones live?”
I said, “Sovereign Lord, you alone know.”
4 Then he said to me, “Prophesy to these bones and say to them, ‘Dry bones, hear the word of the Lord! 5 This is what the Sovereign Lord says to these bones: I will make breath enter you, and you will come to life. 6 I will attach tendons to you and make flesh come upon you and cover you with skin; I will put breath in you, and you will come to life. Then you will know that I am the Lord.’”
7 So I prophesied as I was commanded. And as I was prophesying, there was a noise, a rattling sound, and the bones came together, bone to bone. 8 I looked, and tendons and flesh appeared on them and skin covered them, but there was no breath in them.
9 Then he said to me, “Prophesy to the breath; prophesy, son of man, and say to it, ‘This is what the Sovereign Lord says: Come, breath, from the four winds and breathe into these slain, that they may live.’” 10 So I prophesied as he commanded me, and breath entered them; they came to life and stood up on their feet—a vast army.
11 Then he said to me: “Son of man, these bones are the people of Israel. They say, ‘Our bones are dried up and our hope is gone; we are cut off.’ 12 Therefore prophesy and say to them: ‘This is what the Sovereign Lord says: My people, I am going to open your graves and bring you up from them; I will bring you back to the land of Israel. 13 Then you, my people, will know that I am the Lord, when I open your graves and bring you up from them. 14 I will put my Spirit in you and you will live, and I will settle you in your own land. Then you will know that I the Lord have spoken, and I have done it, declares the Lord.’”
Immediately we can see that not even Ezekiel could prophesy this without the specific request of God to do it. He's bewildered, only able to declare God's sovereignty (v3).
There's no indication whatsoever that this is a general authority given to every believer. You can't just create an army from long-dead people—even Ezekiel didn't do that! It was a vision (v1), and the word was to be prophesied to the Israelites about their return to Israel from exile in Babylon (v11-14). So it was a specific word for a specific people for a specific time.
It was a vision! This wasn't even a physically enacted thing. It was deliberately metaphorical, as God himself explains in verses 12-14. The vision meant that God was going to restore the Israelites back from exile into the Promised land. It was from a metaphorical death—the death of Israel as a nation—to a restoration of that nation. Physically, what was happening was moving the people from Babylon and other lands back to Israel. The creation of a living army of bones was not a physical thing.
Furthermore, there's no other examples of this type of action being done at any other time in Scripture. This further indicates that it should not be an expectation that we could prophesy anything we like as if we had a Star Wars like force.
Once again, what we actually see is Ezekiel moving under the direction of God, in close relationship with him. Ezekiel appears stunned at this—it's not his regular way. This is a picture that reinforces directionalism, and does not support the idea that we can prophesy or command anything.