I think I get what you are saying. The cross certainly is not where Calvinism begins (it is more a solution or means than a foundation). Cavinism begins with the sovereign will of the Father, not the work of the Son.
Yes. This is the essence of my argument and it, pre-creation election as the foundation, is a dangerous place to be. The fundamental, or foundational doctrine of salvation from sin, which is the first item of concern for a guilty sinner, is stated in more than one place in scripture. I will give you two.
1) Isa 28:16 Therefore thus saith the Lord GOD, Behold, I lay in Zion (Jerusalem) for a foundation a stone, a tried stone, (we know now he was tried for 3.5 years) a precious
corner [stone], a sure foundation: he that believeth shall not make haste.
The laying of the stone is speaking of his death and burial.
2) Eph 2:19 Now therefore ye (gentiles) are no more strangers and foreigners, but fellowcitizens with the saints (Jewish believers who were in the building first), and of the household (family through the new birth) of God;
20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner [stone];
21 In whom all the building fitly framed together groweth unto an holy temple in the Lord:
22 In whom ye also are builded together for an habitation of God through the Spirit.
The chief cornerstone is not pre-creation election. Jesus Christ must have the preeminence and the scriptures gives it to him and we must also.
So, the Temple that is being built here is first the Chief Cornerstone, Jesus Christ, on which the whole building rests
second, it is the apostles who were the eye-witnesses and who wrote the record and were the initial preachers of the gospel
Thirdly, it is the framework, which is Jewish and gentile believers collectively
fourthly, the capstone is Jesus Christ and the inhabitant of the temple is the Holy Spirit.
In this manner, Jesus Christ is the beginning and the ending, the first and the last, and this statement is in the context of the NT church of Jesus Christ, which is his body.
There is much more wonderful theology but I will let it rest here for now.
Mt 21:42 Jesus saith unto them, Did ye never read in the scriptures, The stone which the builders rejected, the same is become the head of the corner: this is the Lord’s doing, and it is marvellous in our eyes?
The reason gentiles waer included in this house is because Israel's rulers (the builders) rejected Jesus as the Christ.
Lu 14:15 And when one of them that sat at meat with him heard these things, he said unto him, Blessed [is] he that shall eat bread in the kingdom of God.
16 Then said he unto him, A certain man made a great supper, and bade many:
17 And sent his servant at supper time to say to them that were bidden, Come; for all things are now ready.
18 And they all with one [consent] began to make excuse. The first said unto him, I have bought a piece of ground, and I must needs go and see it: I pray thee have me excused.
19 And another said, I have bought five yoke of oxen, and I go to prove them: I pray thee have me excused.
20 And another said, I have married a wife, and therefore I cannot come.
Samaritans Acts 8
21 So that servant came, and shewed his lord these things. Then the master of the house being angry said to his servant, Go out quickly into the streets and lanes of the city, and bring in hither the poor, and the maimed, and the halt, and the blind.
Gentiles Acts 10
22 And the servant said, Lord, it is done as thou hast commanded, and yet there is room.
23 And the lord said unto the servant, Go out into the highways and hedges, and compel [them] to come in, that my house may be filled.
24 For I say unto you, That none of those men which were bidden shall taste of my supper.
But at the same time I do not think it fair to say the cross is merely incidental to Calvinism.
The cross and resurrection is no more important than the regeneration of the Spirit so a man can believe, as Calvinism teaches, or the gift of faith that must come from the Father, both which precedes any confidence in the cross. The most important doctrine in Calvinism is pre- creation selection by God. The cross certainly is an incidental in Calvinism and Calvinism is another gospel.