2 Timothy 2:18 Who concerning the truth have erred, saying that the resurrection is past already; and overthrow the faith of some.
The resurrection is not past.
It is an “error” for someone to say that it is past. The promise of the resurrection is a continual promise from God, as can be seen in Romans 8:11.
According to Romans 8:11 God will bring about our resurrection while we are in our mortal bodies.
Romans 8:11 But if the Spirit of him that raised up Jesus from the dead dwell in you, he that raised up Christ from the dead shall also “quicken” your mortal bodies by his Spirit that dwelleth in you.
This is called “The Quickening”.
God will bring about our resurrection as we “mortify” the deeds of the flesh.
The “resurrection or quickening” is not past but continues and depends on whether we put to death the misdeeds of our fleshly nature.
Romans 8:13 For if you live according to the flesh, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live. NIV
Regarding this topic, remember that Jesus was crucified during His earthly life, He was “resurrected” on earth, and after that He ascended to heaven.
We are to “walk as He walked”, 1 Jn 2:6.
His followers should also experience the resurrected life during this earthly lifetime. This means that they must put to death the misdeeds of the body in order to experience the “resurrected” life while on earth.
The grace of God teaches us to do this as we continue to humble ourselves before God, Titus 2:11-12 and James 4:6.
Tit 2:11 ¶ For the grace of God that bringeth salvation hath appeared to all men
Tit 2:12 Teaching us that, denying ungodliness and worldly lusts, we should live soberly, righteously, and godly, in this present world;
Jas 4:6 But he giveth more grace. Wherefore he saith, God resisteth the proud, but giveth grace unto the humble.