His infallible Church is in Heaven, and is comprised only of regenerated genuine believers whom The Father has made accepted in The Beloved Son. That is the (spiritual) Kingdom of God.
Om earth there is no single visible "Church" (proper noun) of which He is the Head, and through which He manifests Himself, to the exclusion of other groups assembled in His Name. But there are many thousands of local independent churches comprised of both genuine believers recognized as such by the God-head and in whom the Holy Spirit lives, as well as unregenerated "belivers" who profess loyalty to Christ Jesus, but who as yet have failed completely and put their trust in Him, and thus have not received the gift of salvation. This fallible impure collection of earthly tem[poral assemblies constitute the Kingdom of Heaven (spoken of only in the Gospel of Matthew).
There have been many humanistic attempts to institute a supra-church organization of administrators determined to gain ascendence over the local assemblies of churches and make them no longer independent nor autonomous for the purpos of concentrating political power, but they have all failed and become so depraved that they cannot please the God-head.
The only earthly assembly of believers through which Jesus Christ manifests His Headship and guidance in the Spirit is the local independent autonomous regularly meeting chapter of accountable individuals professing loyalty to, and sole ownership by, the Jesus of Nazareth the Christ of God; inducted into as a disciple by a profession of faith followed by voluntary whole-body immersion in water administered by an authorized agent of the God-head; a meeting characterized by congregating for the purposes of participation in the Remembrance Supper that rehearses the manner of Jesus' cross-death, and for learning how to keep Jesus' commandments watchfully secure by incorporating them in one's thought abd actions; and under the local government of a plurality of spiritually mature fellow-believers who have demonstrated that they have overcome the wicked one, Satan, in their deportment.
The only supra-church authority is the Lord Jesus Christ Himself, the only Head of His local assembled body of believers; not an intervening system of officials inserting themselves between God and the common non-clergy individuals.
I do not believe that anyone clinging to the Calvinistic teachings of double predestination can ever be saved as they reject God’s word
Regarding Jean Calvin the lawyer and the logic-based "ism" named for his theology, truly much of it is as legalistic as Romanism, each for different reasons. The only non-legalistic theology is that offered by assemblies that meet and conduct themselves according to the principles that the church assemblies followed as recorded in the New Testament Scriptures, each local assembly being responsible for its behavior to God alone, as trained by the Apostles who were themselves trained by God-Manifest-In-The-Flesh Jesus. That special delegated commission was not passed on to their followers, the ones who had not been in fellowship and appointed by the Only Infallible Pastor/Rabbi/Master.
Many thousands of such independent stand-alone assemblies have existed since their innovation at Jerusalem in the prototype assembly on the day of Pentecost of 33 Anno Domini. The Jerusalem church of disciples itself became patently fallible, impure, as have all its imitative successors. The same is true of all the disciplers following the original Apostles. Thus the visible churches have kept to Christ's standard only by accepting His Word alone as their uncontested Authority, and not resorting to the filtering of it through the Apostolic (fallible) Fathers and the other (fallible, some very much so) Patristics.
The Holy Scriptures alone are the perfect model, of which the Personification of them is The Lord Jesus Christ, the Only Begotten Son of God, upon Which and Whom we can rely trust for salvation, justification, progressive sanctification (=discipleship), and final glorification of the regenerated believer.
The conduct and resultant outcomes of the Romanist system definitely show that it cannot achieve what it has promised, but in fact historically has fallen far short in doing what it ought to do, and what the widespread truly Christian independent autonomous churches really have done in advancing God's estate on earth. Of late, the decline of Romanistic practices has been abysmal, including the wallowing in sinful activity at the highest reaches of its leadership, We need not say more.
The spiritual Kingdom of God was inaugurated in Heaven with the Church on earth as part of that Kingdom of heaven striving onwards.
The very fact that God protects and keeps His church going despite the strenous efforts of those without and within to destroy it, is proof enough. In contrast look at the various non-orthodox movements - they die out in 300 odd years. That’s what we see now in the “mainline Protestant” groups and we see it in the pentecostals etc. with them heading to non-Trinitarianism (the Oneness Pentecostals)