“Once in Christ, ever in Him.
Having taken up His habitation in the heart, He never removes. None can untie this happy knot.
Who will dissolve this union? Will He Himself? No, He will not; we have His word for it; ‘I will not turn away from them,’ (Jer. 32:40).
But perhaps the sinner will do this mischief to himself? No, he shall not; ‘they shall not depart from me,’ saith their God. (Jer. 32:40)
Can devils do it? No, unless they be stronger than Christ and His Father too; ‘Neither shall any man pluck them out of My hand,’ saith our Lord, ‘And none is able to pluck them out of My Father’s hand,” (John 10:28, 30).
But what say you of death, which parts husband and wife; yea, separates the soul from the body? Will not death do it? No: the apostle is ‘persuaded that neither death,’ terrible as it is, ‘nor life,’ desirable as it is; ‘nor’ devils, those evil ‘angels, nor’ the devil’s persecuting agents, though they be ‘principalities, nor powers’ on earth; ‘nor’ evil ‘things present,’ already lying on us; ‘nor’ evil ‘things to come’ on us; ‘nor’” the ‘height’ of worldly felicity; ‘nor depth’ of worldly misery; ‘nor any other creature,’ good or evil, ‘shall be able to separate us from the love of God, which is Christ Jesus our Lord,’ (Rom. 8:38-39).
As death separated Christ’s soul from His body, but could not separate either His soul or body from His divine nature; so, though the saints should be separated from their nearest relations in the world, and from all their earthly enjoyments; yea, though their souls should be separated from their bodies separated in a thousand pieces, their ‘bones scattered, as one cutteth or cleaveth wood,’ (Psalm 141:7) yet soul and body shall remain united to the Lord Christ.
For even in death, ‘they sleep in Jesus,’ (1 Thess. 4:14); and ‘He keepeth all their bones,’ (Psalm 34:20).
Union with Christ is the grace wherein we stand, firm and stable, as Mount Zion, which cannot be removed.”
–Thomas Boston, The Whole Works of Thomas Boston: Human Nature in Its Fourfold State and a View of the Covenant of Grace (ed. Samuel M‘Millan; vol. 8; Aberdeen: George and Robert King, 1850), 8: 180.