ईश्वरो गुरुरात्मेति भेदत्रयविवर्जितैः ।बिल्वपत्रैरद्वितीयैरात्मलिङ्गं यजेच्छिवम् ॥ १९ ॥
In plain words
The Lord, the teacher, your own Self — offer bilva leaves in which these three are no longer three. Leaves with no second to them: with these, worship Śiva, the liṅga that is the Self.
Close to the Sanskrit
With bilva leaves that are free of the threefold difference — 'Īśvara, the guru, the Self' — leaves that are without a second, one should worship the Self-liṅga, Śiva.