All the saints and teachers who are faithful to the tradition of prayer that stretches back to the Desert Fathers (and beyond!) tell us that individual, recollection-oriented Christian prayer starts with meditation and then progresses to contemplation. Neither of these terms is to be understood in, for example, a Buddhist sense. The terms have distinctly Christian meanings. Maybe we could think of them as technical terms of Christian spirituality.
Meditation is prayer that begins by examining, aspect by aspect, the mysteries of creation or salvation. Maybe we pray the Rosary. Maybe we read the Bible and reflect. Maybe we work out thoughts before Jesus’ presence in the tabernacle. Whatever we do, it is us, imagining, thinking, examining, and then loving, which is the main point. We do this. We meditate.
Contemplation is something else. It passes about our imagining or discursive reflections (motivated by and in love of God). In contemplation, we do little mental work. Instead, the Holy Spirit visits us and helps us to pray in a manner that is not (primarily) imaginative or discursive. This is not to say that this prayer is less than imaginative or less than reasonable. No, it is to say that this new form of prayer passes above imagination and above reasoning or discourse.
Here is yet another, from a letter of Saint Paul of the Cross:
Prayer is not to be made according to our ideas, but directed by the Holy Spirit. It is best to begin your prayer with the mysteries [of salvation especially that of] the Holy Passion, for that is the gateway… But when the soul gets lost in the immensity of the Divinity and caught in the vision of the Infinite Good in faith and fed by love, it should remain that way. It would be serious mistake to turn away to anything else [such as the ideas or plans of prayer we had in mind].
This is phrased very simply. Saint Paul of the Cross says, in substance, this: We are not the greatest participant in our prayer. That is God. So if God gives us another form of prayer, other than the one we anticipated, then we ought to accept the gift. Of course, it is a gift to pass above our own manner of thinking, imagining, and discoursing in faith. So if we have not that gift, we must start by thinking, imagining, and discoursing in faith. But if the Spirit comes and visits us with a higher prayer in faith and fed by love, then we ought to accept it. We will grow much in familiarity with God, love of him, and love of our neighbours.
Mediation is at the service of contemplation, for the latter has in it more transformation of our spirit in the Spirit; in it is more love.