Christians gather because God has appointed the Church as the ordinary means of grace, where the Word is preached, sacraments are administered, and the communion of saints fosters growth in the gospel. Though we may read Scripture privately, the Reformed tradition emphasizes that God uses the public ministry of the Church to nourish his children as a mother nourishes her babes.
In the Reformed tradition, the Church is often called our 'mother' because God has deposited whatever is necessary for faith and order within her. As noted in Institutes of the Christian Religion, God does not intend for us to perfect our faith in isolation; rather, he provides pastors and teachers to edify his people. The 1689 LBCF Ch.26 §12 clarifies that all believers are bound to join themselves to particular churches when they have the opportunity, placing themselves under the care and government of Christ's rule.
We do not attend church to earn our acceptance through moral performance, but to be reminded of what Christ has already achieved for us. We are more flawed than we dared believe, yet more loved in Christ than we dared hope. As stated in Hebrews 10:24-25, we assemble to provoke one another to love and good works, not forsaking the assembly. The Westminster Larger Catechism Q.63 highlights that the visible church offers the 'ordinary means of salvation' and the 'offers of grace by Christ to all the members.'