So true to form, you simply ignore the multitude evidences that excludes the church of Rome from being that church, and assume by "church" that the Lord was referring to one particular organic church, which He was not.
At conversion,
by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit. (1 Corinthians 12:13)
The church to which the Lord is married to, and which the gates of Hell will not prevail against, is not
one particular organic church, as in general these are admixtures of both wheat and tares, esp. in the case of Catholicism as well as liberal so-called "Protestant churches (meaning there is some Hell in such churches), while the corporate body of Christ only consists of believers.
And in reality the church of Rome has become as the gates of Hell for multitudes, and not just the Ted Kennedy types which she infers will enter glory due to the merits of Rome.
Thus in answer to your question, the one true church is the mystical body of Christ which God bought with His own sinless shed blood, (Acts 20:28) which unbelievers are not. But as this body will have visible manifestations, then true churches are those such as,
1. Ordained presbuteros/episkopos, that being one office, and which never are titled "hiereus" which is the word used exclusively for sacerdotal priests. And NT pastors are never described as having a primary unique sacerdotal function, but are part of the sacerdotal priesthood of all believers, for all are called to sacrifice. More
here by God's grace.
2. Like Peter and all but two of the known apostles,(1Co. 9:5) these pastors are normally married, and expected to be, if only to one wife, not two, in contrast to requiring most all pastors to have the gift of celibacy, (cf. 1Co. 7:7) which is a dangerous presumption.
3. Like Peter, they preach of the crucified and risen Lord Jesus, the (Divine) Son of God, that "
To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins," (Acts 10:43) And that thus those who believe, and thus are baptized, shall be saved, (Cf. Acts 2:38)
God "purifying their hearts by faith," (Acts 15:9) which faith appropriates justification, being counted for righteousness. (Rm. 3:10 - 4:7ff)
In contrast to the act of baptism effecting regeneration, and rendering one actually good enough to be with God, and thus needing to one again becoming good enough to be with God thru postmortem "purifying torments."
4. They often are converted under strong preaching which convicted them of sin, of righteousness and of judgment, (cf. Jn. 16:8) and of their desperate need for salvation thru effectual faith, (Acts 2:14-41) expressed in baptism, versus being converted thru a ritual as innocent yet morally incognizant souls who need need and cannot fulfil the stated requirements for baptism, that being repentance and wholehearted faith. (Acts 2:38; 8:36,37)
5. And being converted and taught by manifest men of God, they are to "everywhere preaching the word," (Acts 8:4) that of Scripturally substantiated gospel truths, (Lk. 24:44,45; Acts 17:2,11; 18:28; 28:23; Rm. 15:19) with the veracity of which resting upon the weight of Scriptural substantiation in word and in power.
6. And like Paul, since believers are already "accepted in the Beloved," on Christ's account, and made to sit together with Him in the heavens, (Eph. 1:6; 2:6) thus they preach that "to be absent from the body, and to be present with the Lord, (2 Corinthians 5:8) so that even if the Lord had returned in the first century, then all the believers would have gone to be with the Lord, and henceforth be with Him, (1Thes. 4:16,17) not stuck in some postmortem "purifying torments," until the atone for sins and become purged of character defects in order to actually be with God
But they do await the resurrection of their bodies, as being the only transformative postmortem event. (Rm. 8:23) Glory be to God, and with the judgment seat of Christ being the only
postmortem suffering for believers that Scripture manifestly teaches, that of the loss of rewards and the Lord's disapproval due to the manner of workmanship one built the church with, wheat or tares, directly or indirectly. (1Co. 3:8ff) And which one time event only occurs at the Lord's return, not commencing at death. (1Cor. 4:5; 2Tim. 4:1,8; Rev.11:18; Mt. 25:31-46; 1Pt. 1:7; 5:4)
7. They occasionally ("as oft as you do this") take part in the Lord's supper as a communal "feast of charity," (Jude 1:14) as per the only epistle (besides Jude) in which it is manifestly described, not as the central means of conveying grace, as a sacrament around which all else, including the duties of pastors, revolved, but in which they were to show/declare the Lord's death till He comes," (1Co. 11:26) by taking part in sharing food, testifying to communion with Christ and each member for whom Christ died, versus eating independently, even so that "one is hungry, and another is drunken," and "shame them which have not," (1Co. 11:21). And thus not discerning the body of Christ by treating others as if they were not part of it.
More by God's grace.