In kriya level practice, you use ritual to discover and give expression to this spiritual potential. You see the spiritual as something greater than you. It inspires awe and devotion. You connect with it through honor, propitiation, purification, offering, etc. In particular, as was discussed in the commentary on the last verse, you make yourself worthy and capable of communion with the spiritual through the creation of sacred space, purification and precise observance and performance of ritual.
In charya level practice, you discover and connect with the spiritual through your daily behavior. Here you see the spiritual as something that is present in your life, in everything you do, more as a friend or companion than as something greater than you. This is a closer relationship as it covers how you live, not just your performance of ritual. Thus, in the corresponding verse, Jigmé Lingpa talks about intelligent and skilled behavior (or in conventional Buddhist terminology, the practice of means and wisdom).
Higher levels of tantra are talked about in later verses — union tantra in which you use symbols to connect with deeper aspects of the spiritual, supreme union in which you use energy transformation to precipitate similitudes of spiritual awakening, and great union in which you use sorcery methods to transform your experience of life into spiritual presence.
Unfortunately, the complexity of the practices as well as their dependence on a premodern culture and worldview make them difficult, if not inaccessible, to most Westerners. The language of higher and lower is also misleading. It refers to the degree of subtlety involved, not to which is superior or inferior.
Each of these approaches is a viable spiritual path and the challenge is to find the combination or balance which works for you. In every method of practice (sadhana) with which I am familiar, all these elements are present, explicitly or implicitly. This is part of the wonder and magic of practices in the Tibetan tradition. Every method of practice involves the creation of sacred space (in time, in place, in your physical posture, in your thoughts, feelings and sensation) and the practice of ritual, ways of behaving that support your practice, symbols and representations of the spiritual that you create or employ, and energy transformation and sorcery techniques. In other words, you work with all of them at the same time.