“And because of him you are in Christ Jesus, who became to us wisdom from God, and righteousness, and sanctification and redemption, so that, as it is written, ‘Let him who boasts, boast in the Lord.'”- 1 Corinthians 1:30-31.
“What sort of foundation have we in Christ? Was he the beginning of our salvation in order that its fulfillment might follow from ourselves? Did he only open the way by which we might proceed under our own power? Certainly not. But, as Paul had set forth a little before, Christ, when we acknowledge him, is given us to be our righteousness (1 Cor. 1:30). He alone is well founded in Christ who has perfect righteousness in himself: since the apostle does not say that He was sent to help us attain righteousness but himself to be our righteousness (1 Cor. 1:30). Indeed, he states that ‘he has chosen us in him’ from eternity ‘before the foundation of the world,’ through no merit of our own ‘but according to the purpose of divine good pleasure’ (Eph. 1:4-5, cf. Vg.), that by his death we are redeemed from the condemnation of death and freed from ruin (cf. Col. 1:14, 20); that we have been adopted unto him as sons and heirs by our Heavenly Father (cf. Rom. 8:17; Gal. 4:5-7); that we have been reconciled through his blood (Rom. 5:9-10); that, given unto his protection, we are released from the danger of perishing and falling (John 10:28); that thus ingrafted into him (cf. Rom. 11:19) we are already, in a manner, partakers of eternal life, having entered in the Kingdom of God through hope. Yet more: we experience such participation in him that, although we are still foolish in ourselves, he is our wisdom before God; while we are sinners, he is our righteousness; while we are unclean, he is our purity; while we are weak, while we are unarmed and exposed to Satan, yet ours is that power which has been given him in heaven and on earth (Matt. 28:18), by which to crush Satan for us and shatter the gates of hell; while we still bear about with us the body of death, he is yet out life. In brief, because all his things are ours and we have all things in him, in us there is nothing.“- John Calvin, Institutes of the Christian Religion, Book 3, Chapter 15, Section 5.
That’s the foundation believers have in Christ. Giving up anything we may bring to the table, we cling to Christ.