The Reformed and the Lutherans parted company over the sacraments. Reformed leaders, like Martin Bucer and then John Calvin, genuinely strove to achieve full doctrinal unity with the Lutherans. In the following excerpt from Calvin, you can see his frustration at being lumped together with “memorialists” and other radical views:
They [the Lutherans] pretend indeed to make it their ground of quarrel, that we do not give the sacraments their due virtue. But when we come to the point, some produce nothing but bad names and blind tumult, while others, with a toss of disdain, condemn, in a word, what they never read. That they quarrel without consideration, the case itself shows.
And now for Calvin’s response, which makes for a perfectly concise statement of the Reformed position:
Without making further mention of a man [Luther] whose memory I revere, and whose honour I am desirous to consult, let me declare my opinion simply. …the sacraments are neither empty figures nor mere external badges of piety, but seals of the divine promises, testimonies of spiritual grace to cherish and confirm faith, and, on the other, that they are instruments by which God acts effectually in his elect; that, therefore, although they are signs distinct from the things signified, they are neither disjoined nor separated from them; that they are given to ratify and confirm what God has promised by his word, and especially to seal the secret communion which we have with Christ; — there certainly remains no reason why they should rank us in their list of enemies.
(John Calvin, Tracts and Treatises on the Doctrine and Worship of the Church, volume 2 of Calvin’s Tracts and Treatises, pp. 223-224)
This was written following a joint statement from the pastors of Zurich (heirs to Zwingli) and Geneva, yielding a united front from the Reformed on the sacraments. If you would like to dig further into these issues, I was helped by Herman Bavinck’s discussion in volume four of his Reformed Dogmatics, especially pertaining to “sign and seal” terminology.