When you merge "salvation" which is the free gift of God that comes by grace through faith, with our promised "inheritance" which is also free, you will not be able to see that there are detailed conditions associated with meeting the Lord's expectations in appropriating our "inheritance".
If the Lord gives you a field, seed, water and sunlight that is all free, and instructs you to work the field, he has the expectation that you demonstrate that you understand and bring forth produce, does that mean that it wasn't really free?
If we know that the Lord expects those who receive "salvation" from our death sentence that Adam brought upon the world, and we have an "inheritance" (the "treasure" and "pearl of great price"), then we should joyfully work the field so we can please him so as to receive the reward.
You are correct about confusing two issues. You are merging the two. At "salvation", we are given eternal life from our death sentence and a promise of reward, the kingdom of heaven, our "Inheritance". "Discipleship" is the Lord's expected response to his free gifts of both salvation and our inheritance.
27 And whosoever doth not bear his cross, and come after me, cannot be my disciple.
Jesus is not talking about "salvation". He is talking about those who wish to follow him into the kingdom of heaven. There is a cost of following Him into the kingdom that does not "earn" the kingdom, but demonstrates that we value "the treasure hidden in a field" and do whatever is necessary "to buy that field"...as the parable says...
Jesus continues...
28 For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it?
29 Lest haply, after he hath laid the foundation, and is not able to finish it, all that behold it begin to mock him,
30 Saying, This man began to build, and was not able to finish.
31 Or what king, going to make war against another king, sitteth not down first, and consulteth whether he be able with ten thousand to meet him that cometh against him with twenty thousand?
32 Or else, while the other is yet a great way off, he sendeth an ambassage, and desireth conditions of peace.
33 So likewise, whosoever he be of you that forsaketh not all that he hath, he cannot be my disciple.
34 Salt is good: but if the salt have lost his savour, wherewith shall it be seasoned?
35 It is neither fit for the land, nor yet for the dunghill; but men cast it out. He that hath ears to hear, let him hear.
Those that have received "salvation" will face decisions that cost them as disciples that have rewards (entrance to the kingdom of heaven) or consequences (being cast out).