[annalex]

You know, if someone had a tree that could bear fruit, and asked me for gardeining advice, I would not be telling him what to do with the fruit. I would instead tell him to soften the soil, water the tree, chase off vermin, — things like that. I would not exhort him to constantly check if he has fruit.

If good works were a fruit of already obtained salvation it would not make sense for St.Paul to spend the second half of every letter of his on “fruits”.

[Forest Keeper]

You know, if someone had a tree that could bear fruit, and asked me for gardening advice, I would not be telling him what to do with the fruit. I would instead tell him to soften the soil, water the tree, chase off vermin, — things like that. I would not exhort him to constantly check if he has fruit.

You're assuming a conclusion, i.e., that the tree could produce fruit. The better analogy would be that the person only knew he had a tree and did not know if it was a fruit-producer or not. Paul says to check this. If it is a bad tree, then you can do anything to the soil you want, but it still won't produce fruit. The only way to turn a bad tree into a good one is faith.

If good works were a fruit of already obtained salvation it would not make sense for St.Paul to spend the second half of every letter of his on “fruits”.

It makes perfect sense. Paul knew that the worst position possible to be in is that of a false believer (honest non-believers are in a much better position). He ministers heavily to false believers because they are in the greatest need.